Where Does the Toilet Go on the Existing Stack When Adding a Basement Bathroom?

Roughed-In Plumbing

• During the construction of your home, if the blueprints called for a future basement bathroom, the contractor made provisions for the plumbing of the bathroom. You can find plumbing “stubs” in one area of the basement, unless your house is more than 30 years old. The stubs are capped pipes.

The Vent Pipe

• When you look at the roughed-in stubs, you find a square filled with sand or dirt. Beneath this square lies the capped end of a drainpipe that will connect to a tub or shower. Nearby, you will find a capped toilet flange, over which you will install the commode. An additional pipe, intended for the sink vanity, extends from the concrete floor. This pipe serves as both the drain for the sink and the vent for all three basement fixtures.

Venting the Toilet

• The toilet installs directly onto the flange in the floor. When you install the sink, you attach the sink drain to a “sanitary T” plumbing connection that fits on the top of the drain/vent pipe. This “T” connection allows water to drain downward and provides an additional opening at the top of the “T,” to which you will connect a vent pipe. The vent pipe, which runs between wall studs, extends upward, and you tie it in to the stack that vents the main floor. In the unusual case that the main floor stack is on the other side of the house, you can run the basement vent pipe through a chase or a return-air duct to the attic. At that point, you can attach it to the main stack or vent it separately through the roof.

No Rough-In Available

• In older homes without existing plumbing rough-ins, you can install a basement up-flush toilet that collects the water and waste from the commode, sink and shower, grinds it and then pumps it into the main sewer drain. Because no vent pipe is available, you have to attach a vent pipe to the up-flush collection tank and run the pipe upward, through a stud wall, until you can tie into the main floor stack.