I opened up the closet wall on our top floor to extend the closet and I found a black 3" PVC pipe extending from floor to ceiling and through the attic into the roof line. I am assuming this is a vent, but I am not sure for what. I am thinking either the hot water heater or the basement suite bathroom fan, but neither of these make sense to me as it would have been the hardest and longest way to vent it. Also, coming up beside it are 2 water pipes, the kind that typically carry hot and cold water. I am confused as to why those are there if the PVC is in fact a vent.