The Art of Plunging a Bathtub
Sometimes a completely clogged bathtub drain can be plunged free- using a toilet plunger. Plunging a bathtub drain works by forcing a pocket of water or air through the pipe to break up or loosen the clog- which is most often made up of hair and collections of soap in a bathtub.
To plunge the drain well, place the plunger over the top of the drain so that it covers it completely and forms a tight seal against the tub.
Plunge the drain with quick thrusts, about 10 times. You can also start by filling the tub with a half inch or inch deep layer of hot water, to help tighten the seal around the drain and force the air or water pocket to move the clog.
What can also help get a tight seal is to cover the overflow drain below the faucet. Cover it with a wet cloth, or remove the face plate to stuff a wet cloth just in the opening. This can help create an even tighter seal to make the plunging more effective.