A pop up drain stopper is a mechanical device that raises or lowers a stopper in a sink or bathtub drain. In a sink, the pop-up stopper is typically controlled by a visible rod behind the faucets that you pull up on to stop up the sink or push it down to open it up. Raising or lowering the rod closes the stopper to hold water or opens it up to let the water drain. The same type of mechanism controls a pop-up stopper in a bathtub although the lever is through the bathtub overflow faceplate.
While a pop up drain stopper might look complicated, it is a system of linking rods and levers that is fairly simple to repair or replace if you know what to do. If your bathtub is no longer holding water like it should, it’s possible that your pop up tub stopper needs replacement. It may be possible to remove the linkage, clean it, and see where it is corroded or broken to make repairs.
These types of bathtub stoppers are prone to collecting debris or hair, however, and once you remove it, it may be easier to just replace it with a newer type of tub stopper. While it may seem intimidating, you can absolutely do this yourself without calling a plumber.