Repair most bathtub drain clogs by removing the hair mass that forms on the crosspieces inside the drain. The process often requires removing the stopper or drain screen. Use a stiff wire or an old wire coat hanger to form a hook to remove the clog.
If the tub has a drop-type stopper with a knob that is pulled and turned to drain the tub, remove the stopper by lifting it and turning the knob to release the cap. Remove the setscrew under the cap, and lift the stopper out of the way. Use the wire to reach into the drain and snag the hairball. Complete removal may require several attempts at snagging the hair.
A second type of stopper is the push-lock stopper. To remove these slightly domed stoppers, press down so the stopper springs open. Grasp the shaft, and unscrew the domed top. Try removing the clog with the stopper dismantled to this point, but if necessary, unscrew the shaft, and pull it out of the drain to access the clog.
Many older tubs have the stopper in the overflow tube with a lever on the overflow plate that opens and closes them. These tubs generally have screens over their drains to catch debris, but hair eventually builds up and causes clogs. Remove the center screw from the drain screen, and lift the screen from the drain to fix the problem.