The overflow drain works by allowing air into the drainpipe through the overflow channel. This function helps the basin drain faster, thereby preventing—you guessed it—overflows. The overflow drain is triggered when the basin fills with water past the drain overflow opening.

When the bathtub is filled with water, the overflow drain remains inactive, allowing the water to reach a certain level before coming into play. Positioned just below the faucet and near the top of the tub, the overflow drain is equipped with a small opening that serves as a secondary outlet for water.

A traditional overflow consists of a hole cut into the tub to accommodate a drain that installs on the inside and outside walls which collect excess water and sends it down a tub drain to a P-trap. This style is perhaps the most common in older homes and requires some flexibility in cutting and installing the pipe system.