A leaking shower drain will leave a water stain on the ceiling below, as well as cause more problems with your house unless you repair the drain. You must understand the set-up of a shower drain before you can fix one, including the proper method of removing the drain without breaking it or the drainpipe.
Before you fix the shower drain leak, avoid using the shower. The water stain on the ceiling may not necessarily indicate the extent of the damage in the subfloor between the shower and the ceiling below. Water damage can warp floor joists, short out ceiling lights and ruin drywall ceilings. Standing water in the subfloor can also lead to mould growth. Using the shower, before you fix the drain, will only further contribute to the problem.
Remove the Drain
The drain assembly connects to the drainpipe, which sits below the level of the shower pan or floor. You cannot simply lift the drain assembly out of the drainpipe since the original installer used plumber's putty or PVC cement to keep the connection from slipping. Removing the plumber's putty or PVC cement will require effort and the right tools. Place a drain key in the drain opening after you remove the cover then expand the key to fit the drain for leverage. Clamp a wrench to the top of the drain key and turn it counterclockwise until the drain assembly comes free.
A leaking shower drain is due to a worn rubber gasket. The gasket sits between the bottom of the shower pan and the top of the drainpipe, sealing the opening from water that leaks around the lip of the drain piece, instead of going down the drain opening. You have to push the drainpipe to the side slightly to remove the old gasket and slip a new one into place.
With the new gasket in place, you must reinstall the drain assembly in the drainpipe. Before you press the drain assembly into the drainpipe, though, brush PVC primer and then cement onto the inside of the drainpipe and the bottom of the drain assembly. Press the drain assembly into the pipe then drive the drain piece further into the pipe with a rubber mallet, stopping once the lip of the drain piece sits flush with the shower floor.