I am trying to rebuild one of our load bearing wall. In side the old wall, there is a vent pipe (the one the goes up and stick out of roof) that is connecting to some old, no longer used drain. Above, I am pretty much sure there are no drain connect to it. The pipe goes under to claw space, which we do not have way to access. There is a bathroom about equal distance to this vent pipe and another vent pipe in the other end of the room. How can I test if this vent pipe is in use? If would rather cutoff and seal this pipe because it blocks the studs of the wall.