In this video, This Old House plumbing and heating expert Richard Trethewey shows how to fix a slow draining tub.
1. Unscrew the overflow plate from the end of the tub. Use pliers, if necessary, to pull the plate, linkage rods and stopper out from behind the tub.
2. Feed a drain snake down the overflow hole. Tighten the thumbscrew to lock the snake in place, then crank the handle and push the snake down the drain. Repeat two or three more times, extending the snake further down the drain each time.
3. Turn on the water and check to see if the tub is draining any better.
4. Work the drain snake down the overflow hole, only this time, allow the water to run while you snake out the drain.
5. With the clog cleared, inspect the stopper at the end of the linkage rod. If it appears that the stopper was sitting too low in the drainpipe, raise it by turning the rods to shorten the linkage. Tighten the lock nut to secure the stopper.
6. Reinstall the stopper and linkage and screw the overflow plate to the end of the tub.