Usually a bathtub will have a stopper to keep the water inside the tub from running down the drain. There are many different designs used for this, but one of the more common ones consists of a lever on the tub wall that controls a plunger that cuts off waterflow. Sometimes, however, this will not work correctly, allowing water to drain out. This is an issue that can be fixed with a little work. If you unscrew the trip lever plate and pull it out, you will pull out the linkage and the plunger together with it. Pull slowly and carefully since it is pretty long. If your problem is that the tub isn’t draining at all, it is quite possible that the plunger has come loose and is blocking the pipe. In this case, you will need to fish it out of the overflow hole.

If the linkage is rusting and falling apart, it might be time to invest in a replacement. Otherwise, you can adjust it to get the length right for cutting off water flow. If the linkage is set too short, you will experience leaking.