The drain stopper apparatus for most bathroom sink drains is a pop-up assembly with a small vertical rod attached to a pivot rod below the sink. This lift rod slides up and down through a small hole in the back of the faucet body. The pivot rod moves a linkage inside the drain tailpiece, lifting or lowering the stopper as needed.

Pop-up wastes are popular in modern bathrooms. They have a central plug that opens and closes when you push it. Push once, and the plug pops up to let water drain. Push again, and it closes to hold water in the sink.

The mechanics of a pop-up drain stopper are really pretty simple; the handle of the lift rod sits on top of the sink between the faucets and (usually) behind the spout, When the handle is raised, the pop-up drain closes; when the handle is pushed down, the drain opens.

When you lift the rod on the back of your sink, the drain stopper closes, and the sink fills with water. And when you push down the rod, the stopper opens up, and the water-filled sink drains. If this mechanism is not working well, it’s because there is a problem with the drain stopper or the pivot rod.