To unclog a tub drain there are a number of methods that you can try. However, a tub drain can prove to be more difficult to clear than your standard toilet bowl or sink clog. The tub drain itself can become a major obstacle to clearing your drain. In order to clear the clog, you will need to be able to gain unobstructed access to the drain.
This may require you to disassemble and remove the stopper and any connected components. Do not attempt this if you are not sure how to reassemble your drain stopper.
If you are able to easily remove your drain stopper or if your drain has unobstructed access, the easiest way to unclog a tub drain is with a plunger. As a matter of hygiene, I suggest that you purchase a separate plunger from the one you would use for a clogged toilet. Also, do not buy a plunger with the outward facing flange. This is a great feature for clearing a toilet clog but will only get in your way when you try to clear a tub clog.
When using a plunger, it is critical that you create suction between the plunger and the drain. In order to increase suction, it may be necessary to plug the overflow drain of your tub. This should allow the plunger to create maximum force.
Using the plunger properly should clear the clog within a few minutes. If the drain does not clear and you are certain that the plunger is working properly, you should call a professional plumber to clear the clog. It is possible that something has fallen down the drain and the continued force from the plunger could put your pipes in danger of bursting. This seems to be especially probable if there are small children living in the house.