Tub Overflow — How the Safety Drain Works and Why It Leaks

A tub overflow is the opening in the upper wall of a bathtub that drains excess water before it spills over the tub rim.

What It Is

The tub overflow is a safety drain built into the tub body. It is positioned a few inches below the rim, and when water fills to that level it flows through the overflow opening, down the overflow tube, and into the drain line — bypassing the tub floor drain entirely. This prevents flooding if a stopper is left closed or if water is inadvertently left running.

The overflow opening is covered by an overflow plate — a trim plate that may also house the trip-lever or push-button mechanism used to control the tub stopper. Behind the plate, the overflow tube connects to the tub waste-overflow assembly, which routes water down to the P-trap.

Where It Is Used

Every standard bathtub has an overflow port. It is located on the vertical wall of the tub, centered above the tub drain on the drain end of the tub. The overflow is concealed inside the tub apron (the wall of the tub itself) and is not visible from outside.

How to Identify One

The overflow is the round or oval opening covered by the overflow plate on the interior end wall of the tub, typically 14 to 18 inches above the tub floor. It is distinct from the tub drain at the tub floor. Removing the two screws holding the overflow plate exposes the tube behind it.

Replacement

The overflow tube and gasket behind the overflow plate are part of the tub waste-overflow assembly. If the overflow leaks into the ceiling below, the rubber gasket between the overflow flange and the tub body has likely failed. Replacing the gasket requires removing the overflow plate, pulling out the linkage (if trip-lever style), and pressing a new gasket into place before reinstalling the flange. Full assembly replacement involves accessing the drain piping from below.