How to Install a Sewer Line From a Commode to the Septic Tank

Locate the spot where the pipe for the commode runs to the outside of the house. Drive a wooden or plastic stake into the ground to mark the location. Drive another stake into the ground where the inlet from the septic tank is positioned.

Tie a string between these two stakes and measure the length of the string. Make a note of this measurement. This determines the rate of drop you need for the septic tank pipe. For every 10 feet of pipe, the pipe between the commode and the tank needs to descend 1/4 inch.

Use a spade to remove the top layer of grass along the path of your sewer line. Set the grass aside for reuse. Remove the stakes once you have started the trench. Dig the trench to the required depth for your location. Set the removed dirt aside. Measure the bottom level of the trench as you dig to make sure the bottom level is within the required measurements.

Rinse off any dirt on the septic tank inlet. Apply primer to the nipple on the inlet as well as to the inside of the connecting joint. This connecting joint may be an elbow, 45-degree or even 90-degree bend, depending on your needs. Apply glue to the nipple and the connection, and fit them together.

Cut and size the sewer pipe to complete the run back to the toilet. Saw pieces apart with a pipe saw as needed. Sand any edges that have burrs with fine-grit sandpaper. Dry fit the pieces together to make sure they fit together snugly.

Apply bedding to the bottom of the trench if it's required for your location.

Fit the pieces of the sewer pipe together, first cleaning the connections with primer, then applying the glue and sticking them together. Connect the commode sewer pipe outlet to the rest of the sewer pipe with a flexible rubber coupling. Secure it with the coupling clamps, and tighten the screws on the clamps with a screwdriver.