How to calculate the sewer line slope

Construction rules and regulations when installing sewers require taking into account the angle of inclination of the pipes in relation to the cesspool or septic tank. The efficiency of the entire system depends on how much the optimal angle is. Too steep tubes and high-speed water prevent complete washout of solid waste, and the lack of angle is a gross violation of construction rules, then the solid particles gradually accumulate on the walls and clog the lumen of the tube.

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What is the sewer line slope


Installation of an Autonomous sewer begins with preliminary calculations of the length of the mainline, the diameter of pipes, and their slope. This will determine the speed of the water flow inside and the direction of movement. It is especially important to follow the rules if the sewer is planned to be self-flowing. Gravitational forces will direct the sewage in a natural way to the place where it is stored.


The slope of the pipeline is necessary so that the drains flow under the influence of gravity into the well and do not linger on the walls

The angle of the sewer pipe in a private home depends on the following indicators:

  1. Pipe diameter. The larger diameter of the sewer cleanout pipe, the smaller the slope.
  2. The material from which the pipes are made. The smooth inner surface facilitates the rapid passage of water and debris through the sewer system. Cast iron, asbestos cement, and some types of synthetic materials have a rough surface on which a large layer of silt sticks over time. This reduces the performance of the pipe. Even with a large diameter, the throughput is reduced, and the house is flooded if you do not take measures for cleaning in time. Clean the clogged sewer will have to be regularly, and this is inconvenient the cost of chemicals and the call of a plumber. Homeowners often have questions about why my bathroom smells. The water does not completely descend; it stagnates in the pipes, so there is a smell of dampness, mold, and other unpleasant odors of the sewer.
  3. The layout of the sewer pipe system in the house. The correct plumbing layout- a smaller diameter for drains in the bathroom, shower, and kitchen implies a greater slope of the pipe.

sewer line layout

Proper slope of gravity drainage and sewer pipes is important so that liquids flow smoothly, which helps transport solids away without clogging. A pipe that is too flat will prevent waste from flowing away. It is also commonly thought that pipes that are too steep will allow liquids to flow so quickly that solids will not be carried away.

Drainage pipes are usually run at the minimum allowable slope so that ceilings can be kept as high as possible.

sewer cleanout pipe in the house

According to the International Plumbing Code, drainage pipes should be run with a uniform slope at the following minimum pitches:

According to the International Plumbing Code, drainage pipes should be run with a uniform slope at the following minimum pitches


Large Diameter Sewer Pipe Slopes

Large sewer lines require calculations to determine the proper pitch. Usually, sewer mains should be designed to have a flow rate of 2 feet-per-second during peak dry-weather conditions. Flow rates are usually kept below 10 feet per second. For flow rates greater than 10 feet-per-second, the pipes should be designed with anchors or other means of preventing the pipe from shifting.

Important steps for a proper sewer system

Important steps for a proper sewer system

In addition to the angle of inclination for the correct operation of the drainage system, the absence of sharp and right angles in the connection of pipe parts and turns is important.


Failure to comply with rules of the following issues:

-the gap plumbing joint

-silting of the pipe and the termination of the sewer work, which entails raising the water level in the toilet, the sink and the drain problem in the bathroom;

-odor in the apartment due to the poor performance of siphons;

-a broken pipe and flooding the basement.

clogged sewer line

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Errors in determining the angle of the pipes

The largest number of blockages and failures of Sewerage occurs due to improper design. Non-compliance with the SNiP rules leads to the failure of water gates, unpleasant odors in the room, poor drainage from the sink and bathroom, and silting of pipes. A burst pipe and a sewer spill can lead to infection with pathogens in people, as well as poisoning with toxic fumes.

Error installation is a properly selected diameter of the pipes, no sewer pipes, and ventilation. As a result, low pressure and difficult passage of viscous masses due to poor air circulation in the system.

the plumbing joint

In addition to the slope, poor operation of the sewer system can lead to incorrect angles of joining pipes, lack of seals, the incorrect transition of a smaller diameter to a larger one.

More problems are caused by the incorrect installation of cast iron pipes, in which the sediment is formed faster since they have a rough surface. Stagnation of liquid in one of the sections leads to rotting and leaking pipes.

Plastic communications are less prone to blockages, but even they can accumulate silty sediment if the system is incorrectly designed – choose the wrong diameter or incorrectly calculate the slope. Non-professional workers often try to increase the slope of the pipes, believing that this way the drains will get into the sump faster.

The use of cheap building materials leads to rapid failure. Quality products are checked by special equipment for the presence of hidden cracks, chips, burrs inside. If the manufacturer neglects to check the quality, such products are cheaper, but only the buyer is responsible for them.

It is unreasonable to install powerful cleaning systems in a place where the conditions and soil allow you to clean the drains naturally, without harming the environment.

A crack in the pipeline is possible if the pipes are filled due to an incorrect slope

If you need help determining the correct tilt and position of your pipes, or if you need the help of a specialist in laying them, as well as in estimating the estimated cost of replacing sewer lines, contact your local plumbing companies. Experienced plumbers will help you make a diagram of the slopes of sewer pipes, answer your questions and problems.

When installing sewers in a new building, design and calculations must be performed by specialized organizations that employ engineers. You must have a license for this type of work. It is desirable that the company has experience in local climatic conditions, on this type of soil.