Proper toilet drain installation

Updated March 23, 2017

If you're installing a new toilet, this information will help. A toilet drain is a component of the drain-waste-vent system. The drain-waste-vent system properly drains the water that carries away waste. The drain must be vented properly because odours and gases can accumulate and must go out of a pipe, which exhausts through the roof. The pipe also pulls air into the system to eliminate the possibility of a vacuum in the system.


Cast iron drain-waste-vent systems can be found in many older homes. Lead solder was used to connect the joints. Today, the most common material used for drain-waste-vent systems is polyvinyl chloride or acrylonitrile butadiene styrene, which are rigid-plastic materials. Use glue to seal the connections. To avoid the sound of running water draining through the system, install cast iron pipe in certain locations. Use neoprene to seal cast iron connections. Generally, fittings should be made of the same material as the pipe. If not, install special fittings.

Installation tips

Plan the route to install the piping. Measure the distance from where you tap into the main line to the drain to estimate the amount of pipe needed. Count the type and number of fittings. Remember: at the drain opening, use a closet elbow for the connection to the main drain.

The mount of work required depends on where you install the toilet. Look at the location and run of the existing drain-waste-vent system, and try to plan your toilet drain installation accordingly. Try to locate the toilet drain to minimise as much work as possible. For example, if you are installing a toilet on the second floor, try to position it above a first floor toilet and branch off from the system from this location. If the toilet drain is in the basement, locate the wall main pipe runs.

Whether you work with polyvinyl chloride or cast iron, you support the pipe before you cut into the existing drain-waste-vent system. The soil stack the main pipe in the system has a 7.5 to 10 cm (3 to 4 inch) diameter. Determine a location to cut into the main pipe. Support the pipe before you cut into the existing system.

Once you brace the system and cut the main pipe, install a 10 x 7.5 cm (4 x 3) or 10 x 10 cm (4 x 4 inch) "wye" fitting. This depends on the pipe size. If you are installing polyvinyl chloride in a cast iron system, you will need special fittings. The drain piping must have a continuous downward slope of 6 mm (1/4 inch) for every horizontal foot of pipe.

Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

John Landers has a bachelor's degree in business administration. He worked several years as a senior manager in the housing industry before pursuing his passion to become a writer. He has researched and written articles on a wide variety of interesting subjects for an array of clients. He loves penning pieces on subjects related to business, health, law and technology.