Access your drum trap. This component is usually found under the floor directly underneath the tub. Depending on your home, you may have to remove part of the flooring to get to the trap. You may also gain access from underneath by cutting a hole in the ceiling of the room underneath the tub. If you are unsure of how to access the trap in your home, consult a contractor or plumber.
Pour or spray lubricating oil onto the sides of the drum trap cover once you've gained access. Since the cover is screwed on, focus on getting the oil onto its threads. Let the oil sit for 15 minutes.
Place an old rag over the cover. Tighten a wrench around the cover and turn the wrench to the left until the cover begins to turn. Apply as much force as is necessary to move the cover.
Remove the wrench and the old rag. Unscrew the cover the rest of the way with your hand.