Step 3 · Access and Disconnect Drain Plumbing
To disconnect the tub drain, you must first access the drain and overflow assembly (waste and overflow). Since there is no access panel, you'll need to create one. Go to the wall behind the tub's faucet and drain, and cut a 12x12 inch or larger hole in the drywall between two studs. Use a drywall saw for this. Once you can see the plumbing, use a tub drain wrench (also called a drain key) inserted into the drain crossbars from inside the tub to unscrew the drain shoe. Then, from the access hole, unscrew the slip nuts on the overflow pipe and the P-trap to completely disconnect the drain assembly from the tub.