Any bathtub drain stopper that doesn’t do its job is an annoying inconvenience. Usually, the problem is easy to fix, though the procedures vary depending on what type of bathtub stopper you have. Some drains have stoppers that are spring-loaded, operated by a push of the toe or hand, while others use a trip-lever mounted on the bathtub’s overflow plate. A trip-lever drain stopper is more tricky than most to fix, due to its somewhat complicated mechanism.
How Trip-Lever Drain Stoppers Work
First, it’s important to understand something about how this style of bathtub drain stopper works.
The small up-and-down lever you see protruding from the overflow plate on your bathtub is connected to a vertical connecting rod inside the overflow pipe behind the front tub wall. Near the bottom of the connecting rod is a plunger of some kind—usually a weight that works by sealing the drain opening at the bottom of the overflow tube. This type of drain stopper is sometimes known as a lift bucket.
Sometimes, however, the trip lever operates a horizontal rocker arm that works a pop-up drain plug, which fits into the bathtub drain opening. In this case, the plunger device may be a type of spring that connects to the horizontal rocker arm.
The fixes for both types of drain stoppers are slightly different.
Source: The Spruce