What Is a Bathtub Drain Assembly?

Steven Symes

A bathtub drain assembly is a series of plumbing parts that transport the waste water from a bathtub, feeding the water into a large drainpipe. The bathtub drain assembly is made up of its own series of pipes that are interconnected, and also connect to the large drainpipe. The tub drain stopper is also part of the bathtub drain assembly, which controls when the water can flow out of the bathtub through the main drain.

Water flows out of a tub through the drain.
Water flows out of a tub through the drain.

The main portion of the bathtub drain assembly is a pipe that runs horizontally under the bathtub. This drainpipe is called the drain shoe, which connects to the main drain body you see in the bottom of the bathtub. On the other end of the drain shoe is a pipe tee, which has three openings to connect to the parts of the drain assembly.

PVC is a popular material for bathtub drains.
PVC is a popular material for bathtub drains.

Plumber’s putty or silicone caulk sits between the main drain body and the bottom of the bathtub. Not only do these materials provide a strong bond between the drain body and the bathtub, but they also create a watertight seal so water does not leak around the outside of the drain body, causing it to pool under the tub. When a person needs to remove the drain body, he must twist the drain body counterclockwise with enough force to break the bond, which he can do using a specialized tool called a drain key.

An overflow drain tube runs vertically behind the tub, connecting to the overflow drain opening that sits on the side of the tub, below the faucet’s spout. The overflow tube also connects to the pipe tee, sending water that reaches the height of the overflow drain opening down the main drainpipe, which is the third pipe that connects to the pipe tee.

Not all bathtub drain assemblies use the same kind of drain stopper. In the past, both built-in and pop-up stopper assemblies were popular in bathtubs. Both types have a lever mounted to the overflow drain cover, with the pop-up stopper visible in the main drain body. Built-in stoppers slide up and down the overflow tube, cutting off the flow of water from the drain shoe to the pipe tee. Twist-and-pull stoppers involve a person turning the actual stopper in the main drain body to open and close it.

Different materials can be used to make a bathtub drain assembly. Traditionally, bathtub drain assemblies have been made of metal, such as brass or copper. Plastic or PVC is a popular material today, since it is less expensive and easier to install.

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