Sewerage slope in a private house - what should be. The slope of the internal sewerage The slope of the external sewerage system snip

What is a well-chosen slope of sewer pipelines for a private house? This is primarily 50% freshness in the bathroom. And secondly, a lot of free time that would have to be spent on cleaning pipes. Indeed, with an insufficient slope of sewer pipes, solid particles gradually accumulate in them due to friction forces, which will eventually lead to blockage.

If the slope is too large, the likelihood of leaks will increase, and the noise level will also rise. In addition, the separation of the liquid into fractions is inevitable. In other words, solid particles will sink to the bottom of pipes, since their speed is much less than the speed of water.

Recommended pipe slope values ​​can be found in SNiPs 2.04.03-85 (SP 32.13330.2012). "Sewerage, external networks and facilities" and 2.04.01-85* (SP 30.13330.2012) "Internal water supply and sewerage of buildings". Since they contain information about maximum and minimum pipe slopes for external and internal sewerage. But if the goal is to lay a sewer in a private house to a septic tank or a cesspool, then the last regulatory document will suffice.

The slope of the pipes of the external sewerage

The values ​​of the smallest slope of pipes for external sewerage can be found in paragraph 5.5. SP 32.13330.2012. So, according to him, the minimum slopes of pipelines and channels for the following pipe diameters must be taken:

• 150 mm- from 0.007 to 0.008 (7-8 mm per 1 m);

• 200 mm- from 0.005 to 0.007 (5-7 mm per 1 m).

In general, for gravity systems, this parameter depends on the speed of wastewater movement and does not depend on the total volume of liquid.

As for the maximum slope of pipelines, it is 0.15, provided that the pipe is longer than 1.5 meters.

The slope of the pipes of the internal sewerage

The smallest slope for internal pipelines is determined in the following paragraphs of SP 30.13330.2012. So, clause 8.3.2 states that in non-pressure sewer networks, where the liquid must move by gravity, the slope must be at least 1 / D (D is the outer diameter of the pipe in millimeters). Also in this regulatory document there is clause 8.6.6, which limits the minimum slope of overhead pipelines to 0.005.

The maximum value of the slope of the pipelines here is limited to 0.15 (15 cm per 1 meter). But experts still recommend laying sewer pipes with a slope of 0.04-0.07 or 4-7 cm per 1 meter.

Next, I would like to give two tables in which you can find not only the minimum and maximum slope values ​​\u200b\u200bfor the internal water supply, but also its optimal values ​​\u200b\u200bwhen connected to various sanitary appliances.

Table 1. Limit values ​​​​of the slope of sewer pipes, depending on their diameter.

Table 2. Optimum pipe slope for plumbing fixtures.

Example

Calculation of the slope of sewer pipes

All of the above was the determination of the optimal slope of sewer pipes in a non-calculated way (well, or almost non-calculated). But this parameter can also be found using a special calculation, depending on the speed of the liquid, the diameter of the pipes and the filling level of the pipelines. True, this is very long and tedious process, which is usually resorted to in the case of large sewerage systems (industrial facilities, central sewerage for multi-storey buildings, etc.). Those who are interested can use the formula presented in paragraph 8.3.2. SP 30.13330.2012 or the Callbrook-White formula.

The calculation and installation of sewerage are carried out in compliance with the necessary standards. Only in this way will you get an efficient and durable system. It is especially important to observe the slope of the sewer pipe when installing a gravity system (this is the option for removing wastewater that is used in an apartment and a private house). This parameter depends on the diameter and length of the sewer. It is selected in accordance with SNiP 2.04.03-85 and 2.04.01-85. Insufficient, as well as excessive, pipe slope can lead to many problems. In our article we will tell you what slope of the internal and external sewerage is needed, how to calculate it and what to look for.

To determine the minimum sewer slope, home craftsmen use the following methods:

1. In order not to make a calculation, some masters try to make the angle of inclination as large as possible.
2. Some craftsmen generally miss this moment or make the minimum excess, which is specified in SNiP for pipelines of a different diameter.
3. To correctly determine the slope of the sewer pipe, you need to make a special calculation, guided by the standards from SNiP and other regulatory documents.

As it may seem, too much slope of the sewer pipeline will help the drains to drain faster into the common house system. However, with a very fast flow of effluents, they do not have time to wash away all the solid particles, and they are deposited on the inner surface, forming a blockage. In addition, at high speed, the drains cover the entire lumen of the product and cause a breakdown of the water seal in the siphons. As a result, gases from the sewer pass into the room. That is why even the maximum slope of the pipeline is strictly limited by SNiP.

Important: it is forbidden to make the slope of the sewer pipeline more than 150 mm per linear meter.

The lack of slope or the smallest slope of the sewer pipe can lead to silting of the pipeline. Such a system will not be able to be cleaned naturally during the flow of water. As a result, it will regularly become clogged and require repair, which will significantly reduce the life of the entire sewer.

Attention: in order for the sewer to serve you without breakdowns and for as long as possible, it is necessary to make a preliminary calculation taking into account the norms from SNiP, according to which the excess is selected depending on the diameter and length of the pipe.

Purpose

The angle of inclination of the sewer pipe is made when installing the internal and external systems in the apartment and house, because thanks to this you can insure against many problems during the operation of the networks:

1. If the system becomes silted due to insufficient slope or its absence, then the sewer clearance will narrow, and when a large amount of water is drained, a water hammer will occur, breaking the water seals in the siphons. If there is no water seal in the siphon, unpleasant sewer gases will begin to penetrate into the apartment.
2. Silting of the main pipeline will lead to the failure of the entire system.
3. The normative slope of the sewer pipe will protect against breakthroughs and leaks that form in the basement of the house.
4. If you install cast-iron sewer elements subject to corrosion without tilting, then fistulas and holes may form in the system due to stagnant water.

Important: The inclination of the pipeline is necessary to obtain the optimal speed of movement of wastewater, at which solid particles will be transported to the end point without settling at the bottom of the product. According to the norms of SNiP, the flow rate of wastewater through the system should be 0.7 m / s.

Choosing the optimal value

To calculate the required excess, you need to know the length of the entire pipeline and its purpose. In order not to make a calculation, you can use ready-made tables from SNiP, which gives the standard slope for drain systems from various sanitary appliances:

• For draining from the bathroom, elements of 40-50 mm are used. The maximum distance from the drain to the siphon without ventilation is 1 ... 1.3 m. The slope is 1 to 30.
• The drain from the shower must be made of pipes 40-50 mm. The maximum distance is -1.5 ... 1.7 m. Excess - 1 to 48.
• The drain from the toilet is made from a pipeline measuring 10 cm. The maximum distance is up to 6 m. The slope should be 1 to 20.
• Sink: elements with a size of 40-50 mm, distance - 0 ... 0.8 m, excess - 1 to 12.
• Bidet: products with a diameter of 30-40 mm, distance - 0.7 ... 1 m, slope - 1 to 20.
• Washing: pipeline with a diameter of 30-40 mm, distance - 1.3 ... 1.5 m, excess - 1 to 36.

The combined drain from the sink, shower and bath is made from products with a size of 5 cm. In this case, the maximum distance should be no more than 1.7 ... 2.3 m, and the slope should be 1 to 48.
The optimal and minimum slope for pipes of a certain diameter connected to specific devices is also normalized:

• A pipeline with a diameter of 4-5 cm coming from the sink can have a minimum slope of 0.025 ppm, and 0.35 ppm is considered optimal.
• Products with a cross section of 10 cm, coming from the toilet, should have a minimum slope of 0.012, and the optimal one - 0.02.
• Elements with a size of 5 cm, laid from the sink, may have a minimum excess of 0.025, and the optimal value is 0.035.
• Pipes with a cross section of 4-5 cm are laid from the washbasin and bathroom with a minimum slope of 0.025 and an optimal slope of 0.035.

Excess per running meter

As a rule, the sewerage slope per 1 meter according to SNiP is determined not in degrees, but in a value that is expressed as the ratio of the excess of one end of the pipeline over the other to a linear meter of length.

So that you know what pipe slope to make per linear meter, you can use the following data:

• For elements with a cross section of 50 mm, the minimum value is 0.03 ppm, that is, one edge of a meter product must be 30 mm higher than the second.
• A pipeline with a diameter of 110 mm must have an excess of 0.02. This means that one edge is 20 mm higher than the other with a length of 1 meter.
• The 160 mm piping must have a minimum slope of 0.008 ppm. This means that the excess of the meter section is 8 mm.
• Elements with a size of 200 mm should have an excess of 0.007 ppm, that is, one end of a meter segment is 7 mm higher than the other.

Important: the larger the diameter of the pipeline, the lower the excess value.

To calculate the slope of a sewer pipeline of a certain length, it is necessary to multiply the minimum slope, which is determined taking into account the section of the element, by its total length. For example, the beginning of an element with a diameter of 110 mm and a length of 10 m should be 20 cm higher than the end, since 10 m x 0.02 (minimum slope for a 110 mm pipeline) = 0.2 meters or 20 cm.

Outdoor networks

When determining the sewer slope in a private house, one should not forget about the external network, which must be mounted with a slope to remove wastewater by gravity. Usually, for laying external networks, products of a larger diameter are used than inside the house. When determining the slope, they are guided by the following standards:

1. If elements with a diameter of 150 mm are laid, then the recommended slope is 0.008 ppm. If for some reason it is not possible to observe such an excess, then it can be reduced to a value of 0.007.
2. In the case of laying a pipeline with a cross section of 200 mm, the minimum excess should be 0.007 ppm. It can be reduced if necessary to 0.005.

The indicator of the maximum slope of the external pipeline is also normalized. For elements of any diameter, it cannot be more than 0.15, that is, an excess of no more than 15 cm. With a large slope, the system will not be able to function correctly, as blockages will form.

Occupancy calculation

When performing the calculation, the filling of the pipeline is necessarily found. This value will help determine the speed of movement of wastewater, which is very important for finding the optimal excess at which the system can operate efficiently.

Important: to determine the filling level, the water level in the pipe must be divided by the diameter of the pipeline. The minimum occupancy according to the norms is 0.3, and the maximum is 1.

Having received the level of calculated filling, it is necessary to use a verification formula, that is, to compare the obtained value with the coefficient of optimal filling for elements from certain materials:

• for plastic and glass products it is 0.5;
• for systems made of cast iron, asbestos cement and ceramics, this value is 0.6.

For comparison, the square root is taken from the calculated value and multiplied by the minimum flow rate, which is 0.7 m/s. The resulting number must be compared with the optimal filling capacity of the system (based on the material). It must be greater than or equal to it.

This article discusses in detail such a nuance of installing the system as the correct sewerage slope of 1 meter: SNiP and regulatory requirements that should be followed in practice, optimal performance for certain areas, recommendations for arranging piping. The text contains an overview of common mistakes and tips to help avoid them, and formulas to rely on when designing a sewer line.

To ensure correct and uninterrupted operation, when designing a system, it is necessary to comply with the norms of SNiP

Comfortable living in a country house is possible only if there is a system designed for the removal and disposal of domestic wastewater. For these purposes, an autonomous type sewerage system (centralized for apartments) or a septic structure is used. Inside the system, the movement of the waste liquid through the pipes is carried out in a non-pressure way. In other words, polluted effluents are transported to the place of purification by gravity. This is facilitated by natural gravity, which is achieved due to the slope of the highway.

Important! Natural gravity appears only if the sewer is located at a certain slope. In this case, the system will function normally only if the slope of the sewer for each meter of the pipeline complies with the regulatory requirements of SNiP.

The optimal slope factor also depends on additional factors:

• diameter of pipeline elements;
• the material from which the pipes are made;
• schemes of external and internal placement of sewerage.

Despite the apparent simplicity, as a result of incorrect design of sewage treatment facilities and the wastewater main, blockages and plugs can form in the collectors, and the system itself will not be able to fully fulfill its main task.

How to avoid mistakes when installing sewerage in an apartment with your own hands

When it comes to the slope of the pipeline, it is important not to go to extremes. There are only two types of popular mistakes that inexperienced people make when building sewers.

In the first case, there is no slope of the line or it is not enough to move the liquid by gravity. As a result, the flow rate decreases, due to which the dense fractions are not washed away, but remain on the inner walls of the pipes. There is a gradual accumulation of sediment, which develops into a blockage.

Partially, wastewater with impurities of fractions of various densities lingers on the walls of the main, as a result of which the pipeline becomes covered with silt and begins to exude unpleasant odors that penetrate back into the room. Therefore, you will have to regularly clean the sewers in a private house or apartment, where the system was installed in violation of the requirements.

Excessive inclination of the system can also create the prerequisites for frequent cleanings for preventive purposes. An intense fluid flow at high speed will not be able to capture solid particles from the walls and wash them away. Moreover, in the process of moving water, fecal fractions will layer and be pressed on the walls of the sewer. In this case, all shut-off valves and pipe joints will be subjected to severe stress, which increases the risk of breakage. Therefore, it is very important to adhere to the recommended parameters assigned in the SNiP documents.

Organization of water supply and sewerage: SNiP internal network and external

First of all, the diameter of the pipe affects the throughput of the pipe. Therefore, it is recommended to select the angle of laying the line based on the cross-sectional dimensions of its elements. The larger the diameter of the product, the smaller the slope that is optimal for moving water.

The minimum allowable angles of inclination per 1 m of the pipeline, taking into account its cross section:

If the pipe diameter is 5 cm, then, taking into account the minimum angle (0.02), after installing the system, the difference in height between the placement of the ends of a 1 m long section will be 2 cm.

Important! When distributing sewerage in a private house, it is not recommended to install pipes at an inclination corresponding to the maximum allowable value.

Calculation of the fullness of pipes for the use of SNiP 2.04.01-85 when installing internal sewage

Recommended parameters for arranging internal sewerage are clearly indicated in SNiP. These data are contained in the normative document 2.04.01-85, which can be used as a set of rules and the basis for the construction of a communication system for the removal of effluents.

The calculation of the pipeline fullness indicator is carried out taking into account the characteristics of the material from which the system elements are made. Based on these data, by calculations, it is possible to find out at what speed the sewage water must move through the sewer so that there are no blockages inside the main. The level of filling is taken into account when choosing pipes for the construction of a drainage system.

The following formula is used for calculations:

N=V/D, where:

• H is the level of fullness;
• B - the level of the height of the drains;
• D is the pipe diameter.

The maximum value of the filling level is equal to 1-nitsa. In this case, the slope of the internal sewerage is completely absent, and the degree of filling of the pipe is 100%. The best option for placing the system is an indicator of 50-60%. At the same time, the material on the basis of which the pipe is made, as well as its placement angle relative to the local sewage treatment plant - the septic tank, is of considerable importance.

Products made of cast iron or asbestos cement have a rough surface. The presence of texture on the inside of the pipes ensures quick filling. The main purpose of such calculations is to establish the maximum allowable speed in the drain. According to standard regulations, the minimum speed of movement of the waste liquid is 0.7 m/s. The minimum allowable pipe fill rate is 30%.

Calculation of the speed of movement of wastewater in the internal sewerage network, SNiP and restrictions

For further calculations on free-flow sewerage, the following formula will be required:

V (h/d) ½ ≥ K, where:

• V is the speed of movement of effluents within the system;
• h is the degree of fullness of the pipe (the level of drains in the lumen of the product);
• d is the size of the pipe section (diameter);
• K is a coefficient that depends on the roughness of the inner surface of the pipes and their material, as well as the hydraulic resistance that affects the flow.

For polymer pipes, the reference factor is 0.5. Other materials correspond to 0.6. In practice, the consistency of wastewater and their quantity are not constant values. Therefore, it is far from always possible to accurately observe the filling of the sewerage and the speed of movement of the water flow.

Helpful advice! If it is not possible to perform calculations due to the lack of accurate data using the previously indicated formula, the minimum angle of inclination can be used to lay sections that cannot be calculated. It can be obtained using the formula: 1/D, where D is the size of the outer diameter in millimeters.

The optimal diameter of pipes for arranging internal sewage is 40, 50 and 60 mm. Unlike SNiP, the current set of rules, which was approved in 2012, does not impose restrictions on the maximum angle of inclination of the pipeline. The minimum angle can be seen in the table. For a pipe with a cross section of 80 mm, the coefficient is 0.125.

Arrangement of external and storm sewers: SNiP 2.04.03-85 and its requirements

External sewerage removes waste liquid from plumbing fixtures installed inside a residential building, and also collects rainwater from the site during heavy rainfall due to the storm system. Most often, asbestos-cement and cast-iron pipes are used for the installation of sewerage on the site. The use of polyethylene products with a corrugated texture is allowed.

Pipes intended for the construction of the outer part of the sewer have a large diameter. For their installation, a separate SNiP document is provided with the following requirements:

• if the diameter of the outer pipe does not exceed 150 mm, then the minimum allowable angle of inclination of the line is 0.8 cm per meter of the system;
• the maximum allowable value of the drainage slope does not exceed 1.5 cm per 1 m of sewage;
• if the diameter of the outer pipe is 200 mm, then the value of the minimum slope of the line will be 0.7 cm per 1 m of sewage.

Sewerage slope standards in accordance with the type of device and pipe diameter:

Designing a sewerage scheme in an apartment and installing it

The scheme of the internal sewerage of an apartment or a private house should include devices that are sources of drainage. The list of this equipment consists of a toilet bowl, sinks and washbasins, a bathtub or shower stall, as well as household appliances that connect to the network. The dishwasher and washing machine must be connected to the sewer system and water supply.

For the construction of internal sewerage, it is recommended to use plastic pipes with a diameter of 110 and 50 mm.

SNiP requirements affecting the installation of a waste complex:

• the sewer slope is selected taking into account the diameter of the pipe of the central riser, which is already installed;
• the minimum allowable deviation of the sewer pipeline is 3 cm per 1 r.m., provided that the diameter of the main line does not exceed 50 mm;
• the recommended slope of a pipeline with a section size of 1600 mm is 8 mm per 1 r.m. drain.

Note! The sewerage system in multi-storey buildings is installed in a vertical position. The movement of drains is carried out along the perimeter of the inner walls, while compressed air is in the center of the flow. This approach reduces the likelihood of clogging the sewer.

• it is not allowed to turn the pipeline installed horizontally at an angle of 90º, for this it is better to use corner bends of 45º;
• the use of right angles in a vertical system is strictly prohibited;
• a slight excess of the slope rate is allowed if the pipe length is small.

Features of the installation of autonomous sewerage at their summer cottage

External sewerage is designed to lead contaminated drains towards the septic tank. types of fluid-moving systems do not use gravity. Polluted water is transported to the storage tank using a pump. For these systems, certain SNiP requirements are provided, which specify the maximum distance available for pumping wastewater in this way.

Advantages of autonomous sewers:

• the pressure sewer pipeline runs at a shallower depth than the main of other types of systems;
• there is no need to strictly comply with the slope standards, since the effluents are moved using a pumping station;
• the operation of the system is based on self-cleaning of the inner walls of the pipe, so blockage problems are extremely rare.

The presence of such advantages does not eliminate the need for reconciliation with SNiP when installing sewers. Regulatory documents contain requirements for the optimal placement of a septic tank and other elements on the site in relation to residential buildings, sources of drinking water and other objects. Despite the shallow depth of the pipes, it is imperative to take into account the level of soil freezing in winter.

When working with external sewerage, the relief features of the territory are taken into account. Drainage well structures are recommended to be placed at the lowest points of the site. At the same time, the pipe is laid so that the end of the sewer line is not located below the inlet in the septic tank, otherwise the wastewater will not be able to enter the storage tank by gravity.

Registration of an act of testing systems of internal sewerage and drains

After the installation of internal and external sewerage is completed, a test report is drawn up confirming the functioning of the system and compliance with the standards. This requirement is spelled out in one of the applications of SNiP 3.05.01-85.

To check the operability of the sewer system, the pipeline should be spilled. To do this, at least 75% of all sanitary equipment that is connected in the area to be checked is launched simultaneously. If the installation of the sewer was carried out by the installation organization, such an act cannot be dispensed with.

Data entered into the document:

• the name of the system to be checked;
• name of the construction object;
• name of the general contractor, customer and installation organization, including positions and full names of representatives;
• information from project documentation (numbers of drawings);
• a list of devices open for the duration of the test and the duration of the test;
• data on the presence or absence of defects;
• signatures of the review committee.

Sewer installation can be done independently or by using the services of specialists. In any case, it is important to adhere to regulatory requirements and comply with technology.

It is impossible to lay sewer pipes as you like, for the simple reason that a gravity sewer system is used in a private house. That is, the used water and sewage flow into the treatment plant independently under the influence of gravity.

Such systems have special requirements. One of them is the angle of inclination of the pipes. If the slope is made small, the water will stagnate in the pipe, which will lead to blockage. With a large slope, the liquid flows faster than the heavy fractions that will settle and accumulate on the walls of the pipeline.

In addition, a strong angle leads to noise from the sewer pipes when the water is drained. Therefore, in order for the sewerage system to work without failures, it is necessary to correctly calculate the angle of inclination of the pipes.

Slope calculation

The minimum pipe slope at which the sewer will work effectively can be calculated by the formula: U \u003d L × Y. Where U is the slope, L is the length of the pipe, Y is the minimum slope.

Let's imagine that:

• L = 5 m
• Y=0.07

Then: U = 5 × 0.07 = 0.35 m.

The optimal difference between the beginning and end of a pipeline 5 meters long is 35 cm.

The device of the sewer system is defined by building codes and regulations (SNiP) and should be taken into account even at the design stage of the house. In accordance with SNiP, the optimal slope of sewer pipes with a diameter (Ø) of 50 mm is 3 cm per 1 linear meter. For pipes Ø 100 mm, the slope will be 2 cm.

The table below shows the main values ​​\u200b\u200bof the angle of external sewerage based on SNiP 2.04.03-85 (p. 2.41) and SNiP 2.04.01-85 (p. 18.2)

Outdoor Sewerage Standards

Mounting tilt device

Additional requirements

• For external sewage pipes, the rules provide for a number of additional requirements:
• The maximum slope is 15 cm / m, with the exception of pipeline sections shorter than 1.5 m;
• The bottom of the trenches should be solid, without stones and sharp inclusions. A sand cushion is required, it must contain sand and fine gravel with a fraction of 20 mm. The thickness of the pillow is from 10 to 20 cm;
• The distance from the walls of the ditch to the edge of the pipe is 20 - 30 cm on each side;
• Sewer pipes are laid below the freezing level of the soil, if it is impossible to fulfill this requirement, they are.

Construction guides offer two methods for calculating: according to the formula (described above) and tabular. The table below shows average values ​​for pipes of different diameters.

From the foregoing, it turns out that the optimal slope in the external sewerage network is from 1.5 to 2 cm per 1 linear meter, depending on the diameter of the pipe and material. For the normal operation of the entire system, it is necessary to follow the rules of installation and operation.

Video: sewer slope and their ways of setting

Over the years of designing water supply and sewerage networks, you communicate with many people: with customers, architects, designers, installers, designers of other sections. And the most frequently asked professional question is:

- With what slope should the sewerage be laid?
Of course, the answer to this question must be justified. Well, it is best to look for the basis in the regulatory documentation. Inside buildings, pipes of small diameters are almost always used; we will use SNiP for internal networks.
Clause 18.2 of SNiP 2.04.01-85 * "Internal water supply and sewerage of buildings" says:

"... non-calculated sections of pipelines with a diameter of 40-50 mm should be laid with a slope of 0.03, and with a diameter of 85 and 100 mm - with a slope of 0.02."

For external sewerage, larger pipe diameters are used and they have their own standards. Paragraph 2.41 of SNiP 2.04.03-85 “Sewerage. External networks and structures" says the following:

"The smallest slopes of pipelines for all sewerage systems should be taken for pipes with diameters: 150 mm - 0.008, 200 mm - 0.007."

Well, clearly:

Usually, after silently listening to lines from SNiP on the phone, installers ask the second most frequent question:

- Well, if you really need to make the slope less?
Well, in SNiP there are several reservations on this topic. Regarding the internal water supply, we are talking about "unaccounted sections" of pipelines. In the same paragraph 18.2 of SNiP 2.04.01-85 * there is a formula:

“Calculation of sewer pipelines should be made by assigning the speed of fluid movement V, m/s, and filling H/d in such a way that the condition

here K = 0.5 - for pipelines made of plastic and glass pipes;

To= 0.6 - for pipelines made of other materials

At the same time, the velocity of the liquid must be at least 0.7 m / s, and the filling of the pipelines must be at least 0.3. "That is, theoretically, if you calculate the flow rate of effluents, then filling and, by checking the speed of effluents, you can get some other result.
You can also use the fundamental work of Lukinykh A.A. and Lukinykh N.A. “Tables for the hydraulic calculation of sewer pipelines and siphons according to the formula of A.A. Pavlovsky". By the way, these tables are also suitable for external sewer networks with their large diameters.
However, for pipes 150-200 mm for external sewerage networks in SNiP 2.04.03-85 there is a direct clause:

"Depending on local conditions, with appropriate justification for individual sections of the network, it is allowed to accept slopes for pipes with diameters: 200 mm - 0.005, 150 mm - 0.007."

That is, having the justification “very necessary” and a great desire, you can save as much as 2 millimeters of slope per meter for pipes with a diameter of 200 mm.
Do not forget that, in addition to the minimum slope, there is also a maximum slope for laying sewer pipes. According to clause 18.3 of SNiP 2.04.01-85*

"The largest slope of pipelines should not exceed 0.15 (with the exception of branches from devices up to 1.5 m long)".

That is, a slope of 15 centimeters per meter. If this angle is exceeded during laying, then silting of the sewer pipeline is possible. Or, more simply, the water will quickly leave, and everything else will remain.
Keep the rules, Lord.

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