How Do I Do Rough-in Drain Lines for My Tub?

Decide on the location of the bath tub, if you have not already. In most cases, the bath tub installs in a predefined area in the bathroom, already framed for the tub.

Locate the home's main drain line underneath the floor near the bathroom. Look in the joists below the floor for this drain line. Connect a t-fitting to the drain line and then run PVC pipe from the line to the tub area. Cut into the drain pipe with a hack saw, if need be. Set the drain line at a grade of at least 1/4-inch for every horizontal foot it runs. Use a tape measure to measure this grade.

Connect a p-trap to the drain line at your tub and tighten the p-trap connectors to secure the fitting. Install a t-fitting on the drain line, either before or after the p-trap, which ever works best in your situation, to connect the overflow tube to the drain line. Run the drain pipe from the t-fitting outlet to the tub's drain hole.

Connect the end of the drain pipe to the tub drain hole with an elbow joint. The tub drain fitting screws into the elbow joint to make the connection to the drain. Once the line is run, remove each section, coat the connecting ends with adhesive for PVC pipe and reassemble. Let the entire drain line dry before you use the drain, four to eight hours or as the adhesive manufacturer recommends.