Does a Bathtub Drain Have to Be on the Same Side As the Water Supply?

Standard Tub

• In a standard tub, the location of the drain is just below the location of the water faucet. The bather will sit in the tub with her feet closest to the drain and the faucet. The drain side of the tub is slightly lower than the other side to allow bathwater to drain. You can’t move the drain location because of the slope of the tub, but you can move the location of the water supply although doing so might create an awkward bathing experience.

Water Supply Lines

• The lines that carry hot and cold water from the water supply to the fixtures will run through the walls and the floor joists. If the designated faucet area on your tub is in a tight spot and you can’t access the wall behind the tub, you can usually run the lines in the space beneath the tub. If you have rigid PVC water supply lines that you can access from the far end of the tub, attach flexible water supply tubing to both the hot and the cold PVC supply lines; from there, you can run the tubing to the intended faucet location.

Drainpipes

• The drain configuration is not as easy to adapt as the water supply configuration. The drain beneath a tub must have a P-trap that usually lies in the floor joist space beneath the tub. After the P-trap, the drainpipe must slope downward at a rate of 1/8- to 1/4-inch fall per linear foot of drainpipe. At the soonest convenient point, the drainpipe will tie into the commode drain, and that pipe will then tie into the main house drain.

Plumbing Layout

• Before installing a new tub or other bathroom fixtures, it’s wise to draw a plumbing layout of your home’s existing drainage system to determine how the new fixtures will tie into the main drain. In addition to the water supply and drain lines, the drainpipe that runs from the tub must connect to a vented drainpipe. If a sink drain ties into the same drain as the toilet and tub, the vent will be on the sink drain. If the tub drain does not connect with the other drains within 10 feet, you might have to install a separate vent on the tub drain.