When a tub won't hold water or drain properly signaling a fault with the bathtub drain stopper, the repair is usually straightforward. On many tubs, the stopper is connected to a rocker arm that is, in turn, connected to a handle on the end of the tub by an internal mechanism known as the linkage. Fixing a bathtub drain stopper is often a matter of removing this linkage and adjusting its length or replacing worn and/or damaged parts. In some cases, it may involve removing the stopper and repairing the rocker arm.
The linkage of a bathtub drain stopper is connected to the handle and can be accessed by unscrewing the handle plate and lifting the handle up and away from the tub. The linkage consists of a long U-bracket and a threaded adjustment rod with a weight attached to the end. When the mechanism is working correctly, lifting the handle lowers the weight onto the rocker arm to lift the stopper. If the drain doesn't open fully and the tub drains slowly, the problem can often be corrected by turning the nut on the adjustment rod to lengthen the linkage.
When the tub won't hold water because the bathtub drain stopper doesn't close fully, the problem is could be debris in the drain line or it could be a a corroded or broken spring in the rocker arm mechanism. The design of most stoppers allows them to be pulled out of the drain to make the necessary repairs. The spring on the rocker arm attached to the stopper should be inspected for corrosion and replaced if needed, and the drain should be thoroughly cleaned with a plumbing auger, or snake. The washer around the stopper may also be worn and need to be replaced.
If the design of the bathtub drain stopper does not include a handle, the stopper usually has a self-locking mechanism that keeps it down when pressed and a spring that pops it up when pressed a second time. This type of stopper won't hold water if the washer around the stopper is worn, and the tub won't drain if the spring is worn. If replacement of either becomes necessary, it is usually possible to unscrew and remove the stopper. Most hardware and plumbing supply stores carry a wide enough assortment of bathtub hardware that finding replacements for these essential bathtub parts is not usually a matter of great difficulty.