A bathtub drain uses a trip lever to seal water in the basin or to release water into the drain pipe. Bathtub drains come in two styles: pop-up and plunger. Pop-up drains have a lever that moves the drain stopper up and down. A plunger-type drain assembly uses a lever to move a mechanism with the pipe.
Pop-up drains use an underlying rocker arm to lift the drain stopper. When the lever is released, the stopper moves up, allowing water to drain into the drain pipe. The stopper is visible as it is located at the bottom of the exterior of the bathtub.
Plunger-type drains work in a slightly different way. The drain pipe is covered by a drain guard. Useful for catching hair and debris, this guard does not move up and down but remains fixed in its location. The lever moves an internal plunger in either direction to seal or to release the water that is in the bathtub. The internal plunger is at the end of the linkage and is a metal weight.
Drain assemblies can be identified from the exterior of the tub. If the stopper moves in either direction, it is a pop-up drain. A flat grid indicates a plunger-type assembly.