Our tub is leaking occasionally - we visibly see water accumulate on the celing below. We believe that it is only happening when someone is taking a shower and allowing the water to move down the drain. If we plug the drain - no leak. If we run the shower without anyone in the tub - no leak. If we shower with the drain plugged, fill up the tub, and then get out of the tub before the drain is opened - no leak.

I guess we could shower for the rest of our lives with the drain plugged, but I would rather like to fix the problem. Any ideas? There is no access to the sides or bottom of the tub without opening up walls (tiled walls) or cutting through the ceiling.

This is a common complaint. Does the tub give a bit when you step into it? If so the drain seal may be ruptured allowing it to leak when weight is in the tub. The solution is to unscrew the drain and place a small rope of plumbers putty under the lip of the drain and retighten. You will need a special tool, (see image) to unscrew the drain called a tub drain removal tool. Pick one up at your local hardware store or a plumbing supply house. Good luck, Tom