How to Plumb Rough in Toilets


A plumber "roughs-in" a toilet by installing the waste and vent lines as well as the water supply lines -- in short, everything but the toilet itself. The waste line begins at the toilet flange, which holds the toilet to the floor, and ties into the sewer. Its actual path depends on the configuration of the house and the existing plumbing. The water pipe runs from the nearest cold-water main to a point just below the position of the tank. When the rough-in is complete, the plumber bolts the toilet to the flange and connects it to the water supply.

Things You'll Need

  • Tape measure
  • Toilet flange
  • Pencil
  • Reciprocating saw
  • Screwdriver
  • 3- or 4-inch ABS pipe
  • Waste fittings
  • ABS cement
  • 2-inch ABS pipe and fittings
  • 1/2-inch copper pipe and fittings
  • Soldering equipment
  • Pipe clamp
  • Wood screws
  • Angle stop
  • Wrench
  • Measure the position of the toilet drain hole from the back and side walls. The optimum distance from either wall may be specified in the installation instructions for your specific toilet. If not, 12 inches is the default distance from all walls.

  • Trace the outline of the pipe attached to the bottom of a standard toilet flange on the subfloor and cut out the outline with a reciprocating saw, making the hole slightly larger than the pipe so the pipe will fit easily. Insert the flange pipe through the hole and screw the flange plate to the subfloor with the screws that came with it.

  • Plot the path of the waste pipe from the flange pipe to the nearest vertical toilet drain, also called a soil stack. If there is no stack available, install one by cutting into the sewer at a point just below the toilet and gluing in a sanitary tee that fits the sewer and the waste pipe you are using. Run the pipe vertically to the point of connection with the waste line.

  • Run 3- or 4-inch ABS waste pipe from the bottom of the toilet flange to the waste stack. Connect to the stack by gluing in a sanitary tee at a point which allows the waste line to maintain a minimum slope of one-fourth-inch per foot. The fittings you'll need to run the waste line will depend on the configuration of your house.

  • Glue a reducing fitting to the top of the soil stack to reduce its diameter to 2 inches. Run 2-inch ABS pipe from that fitting through the roof to provide venting for the waste pipes. If you are tying into an existing stack, it should already be vented.

  • Locate a suitable cold water pipe near the toilet. Turn off the water, cut into it with a hacksaw and solder on a tee. If you choose a three-fourth-inch water line, use a three-fourths- by one-half-inch reducing tee so you can run a one-half-inch copper pipe to the toilet.

  • Assemble the water line with appropriate fittings to bring it to a point just below the location of the toilet tank. Run it beside a wall stud and extend the end horizontally about 2 or 3 inches from the wall. Clamp the pipe to the stud with a pipe clamp and wood screws to hold it securely.

  • Install a half-inch angle stop, or shut-off valve, on the end of the pipe. Some angle stops can be soldered while others have a compression fitting that must be tightened on with a wrench. When the angle stop is installed, make sure it's off before you turn on the water and check for leaks.

Tips & Warnings

  • Code requirements for a toilet rough-in are strict, and no single configuration will work in all situations. Make a diagram before you start, indicating pipe sizes, layout and all the fittings you plan to use, and check it with a licensed plumber.
  • Some communities require rough-ins to be conducted by a licensed plumber, and most require a permit and an inspection.

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