need help detecting the source of a bathroom ceiling leak

[starfish11040]

This morning, quite a bit of water came down through a tenant's bathroom ceiling. It seemed to coincide with the upstairs tenant, whose bathroom is directly above, taking a shower. There was no water on the upstairs bathroom floor.This means to me that there are two possibilities: either the bathtub drain pipe is leaking or the shower water is going through the tiled wall.
So I had them do a test. First, the bathtub faucet ran for 10 minutes. No leak.
Then the shower was pointed at one of the walls for 10 minutes. No leak.
Then the shower was pointed at the other wall for 10 minutes. No leak.
There was a leak in the same ceiling about a month ago, We did the test, and water leaked when the shower was pointed at one of the walls. I had it regouted, tested it again and the problem was solved. Now it's happened again but I can't recreate the leak to determine its source.
This is puzzling. Any ideas?

 

[johnjh2o]

By chance were they using the tub? If they filled the tub to the overflow that may be leaking were the overflow gasket meets the tub. (just a thought)

John

 

[starfish11040]

By chance were they using the tub? If they filled the tub to the overflow that may be leaking were the overflow gasket meets the tub. (just a thought)

John

No, the tenant was taking a shower, not a bath.

 

[kouvakis]

cut a whole in the ceiling. stick you head up there and look around. you will be amazed at what you will see. if the leak continues you will have to replace the ceiling anyway. you might have to take our the tile and grouting and replace with fiberglass/resin/plastic tub surround that will withstand movement in the structure.