I have a leak in my shower drain, and I am fairly confident it is between the two screw-in pieces of the drain. The problem I have is it is an upstairs shower, so I do not have access to the floor plumbing at the moment (I may have to start cutting some ceilings :-). Even if I did, the assembly is all PVC, so the bottom (nut) piece is glued to the main drain pipe trap, which means it cannot be turned. My only hope is to figure out how to tighten the male piece from the top (inside the shower). Is there a tool to make this happen? There is nothing I can see to get a grip for turning it. The reason I think this is the problem is because the top lip of the drain is slightly higher (less that 1/8") than the bottom of the shower. That leaves just enough space for small amounts of water to remain in the bottom of the tub. I think the water is actually going down the side of the drain, because those small amounts actually go away over a short time, while it does not appear there is any way for it to actually flow into the drain from outside that lip. Any suggestions?

"(I may have to start cutting some ceilings :-). Even if I did, the assembly is all PVC, so the bottom (nut) piece is glued to the main drain pipe trap, which means it cannot be turned. My only hope is to figure out how to tighten the male piece from the top (inside the shower). Is there a tool to make this happen? There is nothing I can see to get a grip for turning it. The reason I think this is the problem is because the top lip of the drain is slightly higher (less that 1/8") than the bottom of the shower. That leaves just enough space for small amounts of water to remain in the bottom of the tub. I think the water is actually going down the side of the drain, because those small amounts actually go away over a short time, while it does not appear there is any way for it to actually flow into the drain from outside that lip. Any suggestions?"

The drain's secured by a large nut on the bottom, ( see photo) since the drain's glued in you can't turn it. You have to open up the ceiling, (Make a square cut and save the old piece, you can tape it in and patch later) and first loosen the nut so you can raise the drain lip and clean out the old putty seal. Now make a rope of plumbers putty and run it around under the drain lip. Tighten the nut untill the putty no longer squeezes out.
If the shower floor "gives" a bit when you step in it then that's why the seal broke. The shower floor should be shored up with wood or bedded with mortar or cement or this is liable to happen again. Good luck, Tom