How To Clear A Main Sewer Line Clog Yourself

Calculate the Slope

Pipeline being installed in forest — William Taufic / Getty Images

The elevations and the length of the pipe run are used to make the initial slope calculations. Subtracting the ending elevation from the starting elevation yields the total drop in elevation. Dividing the drop by the total run (length) of the pipe yields the slope.

For example, if the pipe meets the city main at a depth of 6 feet and it starts at the house at a depth of 4 feet, the total drop is 2 feet. If the pipe run is 80 feet, the slope is:

2/80 = 0.025 or 2.5 percent

The standard minimum slope for laterals (in most areas) is 2 percent, or 2 feet of drop per 100 feet of run. The actual slope can be slightly steeper than this target but must meet the requirements of the local code. A slope that is too steep will cause the liquids to run faster than the solids, leading to clogs. A slope that is too shallow does not create enough velocity for proper drainage.

Dig the Trench and Lay the Bedding

Sewer Construction — Wicki58 / Getty Images

Trenching for a sewer lateral must be done carefully to prevent unnecessary disturbance of the soil. Any disturbed soil must be thoroughly compacted to minimize settling. In most cases, it's best to make the trench as narrow as possible (to minimize soil disturbance), but this requires precise knowledge of where the pipe will terminate. Sometimes a wider trench is necessary.

The bottom of the trench must be smooth and compacted and must follow the desired slope. Often, a bedding material, typically sand, is laid in the trench to provide continuous support for the pipe. Sand is also much easier to slope than soil, allowing for fine-tuning of the slope before the pipe is installed.

Install the Pipe

Sewer pipeline under construction — Victoria Snowber / Getty Images

Sewer pipe is installed one section at a time, typically starting at the lower end of the pipe run and working up to the higher elevation. Modern sewer pipe is made of PVC and is joined either with gasketed fittings or with solvent glue. Standard pipe size for residential lines is 4 inches. The local code specifies the required pipe material and size.

The bell (female) end of each pipe section should face uphill to minimize the changes of leaks at the pipe joints. The pipe connects to the city main per the city's specifications. At the house end, most codes require one or two cleanouts to provide easy access to the pipe for scoping or for cleaning with a sewer auger.

Backfill the Trench

Heavy equipment beside pipeline — Tetra Images - Dan Bannister / Getty Images

After the sewer lateral is completely installed and passes final inspection, the trench is backfilled to complete the project. The backfilling process often begins with a layer of sand to protect the pipe and eliminate any voids around the pipe. Then, the trench is filled with soil added in layers. Each layer of soil is carefully compacted to prevent settling in the future.

It is always a good idea—and often required—to install a warning tape over the first layer of compacted soil. This alerts crews to the presence of the pipe to prevent accidental damage when doing any excavating in the area.