How to Install Toilet Waste Pipes

Installing new plumbing requires some effort and attention to detail.

Toilet waste systems depend on gravity to remove waste from the house. These pipes must have sufficient drop from the toilet to the sewer or septic tank. There cannot be any sharp turns, level sections or rough places inside the pipes. Proper venting ensures that gas in the pipes does not cause backups. Larger-diameter pipes provide better flow, and for toilet waste systems, pipes are usually either 3 or 4 inches across. When installing toilet waste pipes, it is important to take all of these factors into consideration.

Step 1 – Plan where the new pipe will run. The distance from the new toilet to the main waste line should be as short as possible, to simplify installation and operation. The main waste line is the large (usually 4-inch) line that connects toilets to the sewer or septic system. It runs from the furthest toilet to the sewer or septic. Make a sketch of the system and include measurements.

Step 2 – Measure the components carefully. Lay out all of the pieces and be sure you have enough couplers and elbow pieces, in addition to pipe.

Step 3 – Cut and fit the pieces of pipe together, but don’t glue them yet. Start at the main waste line and work back toward the toilet. Cut and fit one piece at a time. Place the T section 48 inches or less from the toilet. Once all pieces are cut and the pipe is correct, prime and glue each section together.

Step 4 – Install the 2-inch PVC pipe for the roof vent in the 2-inch opening of the T section. The pipe must reach from the waste pipe through the roof of your home and should extend 8 to 12 inches. Remove a section of wall and cut a hole in the roof for the pipe. Run the vent pipe up inside the wall and out through the roof. Allow all cemented joints to dry completely.

Step 5 – Pressure test the system. If necessary, rent a small air compressor and fittings. Block all openings in the pipe assembly with airtight plugs. Attach the test assembly to the 2-inch pipe. Pressurize the system with 5 pounds of air pressure. Wait 15 minutes. If the pressure holds, the system has no leaks. If the pressure drops, locate and repair any leaks, then retest. Once there are no leaks, remove all airtight plugs.

Step 6 – Cut the main waste line and insert the 4-inch transition pipe. Place it low enough so that the new waste pipe has the correct drop. Minimum drop should be 1/4 inch per foot. Connect the new line to the main line via the transition pipe.

Step 7 – The new waste pipe should come up to the level of the bathroom floor. Install the flange on the waste pipe so that the flange rests on the floor. Install a collar on the roof vent pipe. Replace the section of wall you removed in step 4.