Pour 1 cup of baking soda, followed by 1 cup of vinegar down the tub drain. Cover the drain. The solution will fizz up and eat away at the obstruction slowing your tub drain. After 15 minutes, pour 1 gallon of boiling water down the drain to clear it out. Repeat if the drain remains slow.
Use a commercial unclogging solution. Commercial solutions include chemicals that help to dissolve and break apart the obstructions, offering a stronger unclogging solution than the homemade solution. The directions will vary, but typically, the solution is poured directly down the drain and must set for at least 15 minutes before washing away with warm tap water.
Use a plumber's snake to dislodge the obstruction. A plumber's snake (or auger) is a steel cable that extends down the drain (via a hand crank) to push through or pull out the obstruction that is cause your tub to drain slowly. Depending on the type of drain your tub has, it may be difficult to snake the cable down the drain.