How to add toilet plumbing to a sewer line

Written by steve sloane
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How to add toilet plumbing to a sewer line
A toilet requires a sewer pipe to connect it to the main sewer line. (toy toilet image by Wayne Abraham from

Sewer lines for toilets start with a flange under the toilet. A flange is a pipe with a flat circular base at one end with holes in it for screws. The flange is pushed through a hole in the floor and attached to a 90-degree coupling. The coupling is attached to a two-inch diameter sewer line. This sewer line is then attached to the existing sewer line (usually three or four inches in diameter) using a coupling with a two-inch pipe coming out of the side.

Skill level:
Moderately Challenging

Things you need

  • ABS toilet flange
  • ABS 90-degree elbow joint
  • 2-inch ABS pipe
  • ABS glue
  • Hacksaw
  • Tape measure
  • ABS coupling with two-inch pipe on one side
  • 1 5/8-inch galvanised screws
  • Screwdriver

Show MoreHide


  1. 1

    Measure the diameter of the flange pipe and cut a hole in the floor slightly larger than this diameter; make sure that the hole is placed in the correct location by following your toilet's installation instructions. Push the flange down into the hole until the flat base rests on the floor. Spread Acrylonitrile Butadiene Styrene (ABS) glue on the bottom of the flange pipe and on the outside of the male end of the 90-degree elbow joint. Push the glued end of the elbow joint into the bottom of the flange and hold it in place for 30 seconds.

  2. 2

    Turn the female end of the elbow joint so that it faces the existing sewer line (pipe). Connect the elbow joint to the existing sewer line by cutting new two-inch sewer pipe and connecting couplings as required, until you reach the existing sewer line. After cutting through new sewer line, always remove all burrs with a tradesman's knife before gluing. Also remember to glue both the end of the new sewer line and the inside of the coupling before connecting them to each other. When you reach the existing sewer line, cut the line (two parallel cuts to accommodate the coupling with the two-inch pipe coming out of one side) and glue and install the coupling to the existing sewer line. Now glue and attach the new two-inch pipe to the new coupling.

  3. 3

    Screw the flat base of the flange to the floor with 1 5/8-inch galvanised screws. The new sewer line is complete and the toilet is now ready to install.

Tips and warnings

  • Sewer lines require a gradient for waste to travel down. Check with your permit office for the required gradient in your area. If the existing sewer line is much lower than the elbow joint, you won't have to worry too much about this issue.
  • Always verify the required diameters of sewer pipes with your local permit office. However, two-inch sewer pipes are usually used for toilets.
  • Sewer pipe couplings come in straight, 30-, 45-, 60- and 90 degree angles to help you install your sewer line.
  • If you are using PVC sewer pipe and not ABS pipe, you need to first prime all the areas that need to be glued. Make sure that the primer is dry before applying glue to the primed areas.

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