Built-In Versus Pop-Up Stoppers
Built-in and pop-up stoppers work to keep water from going down the bathtub's drain pipe, until you press on the stopper's control lever and allow the water to drain. You can easily see a pop-up stopper in your tub's drain opening as it moves up and down, although you do not see the mechanism that raises and lowers the stopper. You cannot see built-in stoppers since the entire assembly, including the stopper itself, is housed in the bathtub's overflow drain.
Removing the Assembly
With built-in and pop-up stoppers, the first step to fixing the stopper is to remove the screws that hold the overflow drain plate in place. Pull the plate away from the drain opening. For a built-in stopper, you must remove the entire linkage assembly from the overflow drain, as well as the plunger or stopper that should be attached to the bottom of the linkage. When fixing a pop-up stopper, you only need to pull out the linkage enough so that you can reach the nut on the linkage.
Adjusting Pop-Up Stoppers
Once you have exposed the nut on the stopper's linkage, twist the nut to either lengthen or shorten the linkage assembly. Making the linkage longer will cause the stopper to sit higher in the drain opening, while making it shorter will cause the stopper to sit lower in the drain opening. You also must pull the stopper and the arm that is attached to it out of the bathtub's main drain. Clean the stopper and its arm using a rag, and then turn the nut on the bottom of the stopper to adjust how it sits in the drain. Also check the rubber seal that sits around the rim of the stopper, looking for signs of wear or cracking. Replace the stopper's parts, including driving the screws back into the overflow plate.
Adjusting Built-In Stoppers
Built-in stoppers only require you to turn the locknut on the linkage counterclockwise to loosen it, allowing you to rotate the plastic sleeve on the linkage to lengthen it. Reattach the brass plunger or stopper to the end of the linkage if it has become detached. Insert the end of the linkage through the loop at the top of the plunger, and then pinch the end of the linkage closed around the plunger's loop using a pair of needle nose pliers. Lower the plunger and linkage back into the overflow drain and drive the screws through the drain's plate.