Hi. We were having a frequent drip show up on our stairs from the master shower above. The tiled floor of the shower (over concrete pan) had mildew in the corner, so I cleaned out the corner and found water between the tile and shower pan membrane. I initially poured water down the drain and I did the "cover the drain and see if the water level changes test". Neither were conclusive. I pulled out the lower rows of tile and water came out. I also took up the showers tile floor. We've been just ignoring the shower fix for awhile, but today, I realize that if I hold a bucket under the shower and run it, a dark damp patch appears and grows on the concrete. I also opened a hole in the wall of the bedroom and the vertical pipes are not leaking. Did I mention that SO what is happening? It's obviously with a pipe, but what pipe? Do I have to take out this concrete shower pan? Thanks.