"We have a leak from our upstairs bathrooms. We've had trouble on and off for years but credited kids splashing, etc. Recently, my father installed a new tub in one of the bathrooms. From that point onward we had a huge leak in the downstairs kitchen whenever anyone took a bath as soon as they drained the bath. The water shifted, though, from through a central ceiling part to coming through the top of a kitchen cabinet. (sidenote: we also had a repair man fix the ceiling as the tub was replaced, so that area is probably stronger now. The water might be going to a different place because of that.) I closed off that bath and insisted everyone use the shower in the master (1 foot away) until we could afford to have the situation checked out. I can tell we are still having leak problems because the top of the cabinet I can see from the floor is still damp. Question: Is there probably a connection spot between the two showers that are essentially back-to-back that could be leaking? I'm not a plumber, but I would think water pressure from a bath draining would be much more substantial than the shower draining and would cause the flood of water as opposed to what seems to be a constant leak? Help. We're broke and don't have another shower option available."

For openers you MUST localize the leak. If you do not have a access panel in the wall behind the tub I advise you to cut one in. '
Now take a wad of toilet paper and start at the connections from the drain start patting around the joints. At the first sign of moisture stop and let me know what you found. Good luck, Tom