I just cut out a section of a wall in my home to stop a pipe from knocking. It was a real thick PVC pipe, which I now think must serve as the central drain pipe for all of the upstairs bathroom appliances. From that hole though, which I cut about mid-way up the wall (it’s about 10 feet high), I could not see drain pipes for other appliances (I guess maybe I could if I cut more holes). SOmebody told me perhaps the upstairs sink, and bath, and toilet drain pipes come through the floor, but then run horizontally and feed into that fat drain pipe. So, does that make sense, is everything essentially connected? Thank you.