I've got an old shower stall that appears to be 40+ years old. Its got the metal lathe on the walls with concrete floated over it and tile laid on top. Whoever built it did a dang good job because the only place it appears to be leaking is around the drain and a little down the copper supply lines, which I'm assuming is from a leaky valve. All the wood below it is dry and original. I'm considering cutting a hole big enough to put in a new valve and then covering it over. And I think I need to replace the drain while the ceiling is opened up ( this bath is on second floor ). The drain is old cast iron I think. How do I get this thing out? Is it a screw type fitting? Do I need to chisel it out from above? What's the process here?