How to Run a Tub Drain to the Toilet Soil Stack

Measure the total distance from the end of the toilet flange, the flange installed on your bathroom floor under the toilet, to the drain stack with a tape measure. This will give you an estimate of how much PVC drain pipe you will need to reach the stack. Account for any bends or turns you need to make based on your home's plumbing set up.

Set the first length of pipe into the toilet flange joint and run it to the soil stack. Install pipe supports on the joists to support the pipe if necessary, using 2-inch nails and a hammer. Cut the drain pipe to size as necessary and fit any elbow joints required to make your run to the stack.

Set the pipe at a 1/4-inch-per-foot grade all the way to the stack. Use a tape measure to accurately set the grade. The pipe must drop 1/4 inch for every horizontal foot it runs. Adjust the supports as needed to raise or lower the pipe.

Mark the intersection of the drain pipe and the soil stack with a marker. Cut into the stack with a hack saw to separate the stack pipe. Insert a t-fitting between the two sections of soil stack pipe and insert the toilet drain pipe into the other end of the fitting.

Check the grade once again with the tape measure and adjust the supports as needed. Take the entire run of pipe apart and then assemble it again, this time adding PVC cement around the edge of the pipe and fittings before you put them back together. Let the installation dry for up to eight hours or as suggested by the PVC cement manufacturer.