I have a leak in a waste water pipe which manifests itself by dripping water onto my concrete basement floor. The water appears to be running down the outside of the vertical pipe that comes through the subfloor (ceiling of my basement)and makes a 90 degree turn to the horizontal pipe running out of the house. This vertical pipe takes the waste from the second floor of my two story house. Since this pipe is behind a wall on the first floor and runs above the ceiling in my first floor I can't see where the leak originates. Any suggestions on how to decide where to start cutting holes in the sheetrock. Do I start in the wall or in the ceiling.
Thanks in advance for any suggestions.