How to plumb a new toilet

Updated February 21, 2017

Plumbing is one part of maintenance that not many homeowners like to tackle. However, installing the plumbing for a new toilet does not have to be difficult. As with most projects, the right combination of tools and knowledge goes a long way. As long as the existing plumbing is accessible, you are in good shape. Keep in mind that there may be city codes that prevent homeowners from doing this type of home improvement.

Choose a spot for the new toilet. Mark the area and draw a circle large enough for the flange to slip into once the hole is cut. Drill a hole for the jigsaw blade to fit through. Cut the hole out with the jigsaw.

Be certain the flange's extension is long enough to clear the floor and sub floor before securing it to the floor. If not, add an extension to the end of it. Prime the connection first, then apply the glue. Fit the pipe together with a slight twist.

Install an elbow to the end of the flange under the house; use primer first, followed by glue. Layout the approximate amount of each section of drain pipe that is needed under the house. Cut the pipe with a skill saw, cleaning off any burrs that the saw leaves behind.

Locate the area of the existing drain pipe where the tie-in will take place. When the new pipe gets close enough to be precise, cut a section from the existing pipe with a skill saw or reciprocating saw for the sweeping elbow to tie in. Clean the burrs and use primer and glue accordingly.

Suspend the pipe from the floor joists by wrapping a plumber's strap around the pipe and securing it to the floor joists. This will keep pressure off the joints and help you maintain the descent needed to keep the water flowing.

Install an in-line vent if there is no vent to tie into in the wall behind the new toilet. See "How to Install a Bathroom Drain Waste Vent System" in the References section below.

Close the valve that brings water into the house. Locate a cold-water line that is close to the new toilet installation.

Cut into the PVC cold water line with a PVC cutting tool. If the pipe is copper, use a pipe cutter designed for copper pipe. See "Soldering Copper Pipe" in the Reference section for further instructions on how to install copper pipe.

Install a Tee in the spot where you cut the line. Secure as many PVC cold-water lines as needed to the Tee to route the water line to the spot under the house where it will turn upward through the floor.

Drill a hole through the floor that's large enough to slip a water line through. Slip a section of the water line through the hole, then secure it to the elbow that leads into the house. In the house, cut the line to the needed length. Install a threaded end to the line. Remember to use primer first, then glue.

Wrap the threads of the PVC pipe with Teflon tape. Install a shut-off valve on the threads. Secure a water-supply line to connect the toilet tank to the water.


Cut and join as much PVC pipe as you can before crawling under the house. Where gloves and eye protection anytime you work under the house. If floor insulation is present, take care not to dislodge it.


Do not leave power tools unattended in the presence of children. Do not use the PVC primer and glue without proper ventilation.

Things You'll Need

  • Variable-speed drill
  • Jigsaw
  • Toilet flange
  • Schedule 40 PVC drain pipes and fittings
  • PVC primer
  • PVC glue
  • Plumber's strap
  • Roofing tacks
  • PVC cold water line
  • PVC threaded adaptor
  • PVC cutters
  • Teflon tape
  • Shut-off valve
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About the Author

Michael Straessle has written professionally about the construction industry since 1988. He authored “What a Strange Little Man,” among other books, and his work has appeared in various online publications. Straessle earned a Bachelor of Arts from the University of Arkansas at Little Rock in professional/technical writing.