(This image is a cross section of the floor joist.) I am replacing a tub and have opened a can of worms in the process. This is all pre-existing work, so I am not looking to redo it at this point, however I'd to keep water out of that vent line. When I cut it open, it had water inside, and it has no place to go, since the vent line simply goes up and through the roof about 10 feet away. Before I touched this, it was simply connected together with a very small bend, not enough to stop much flow. I am thinking of using maybe a studor valve or loop vent, but I am not sure. Just want to replace a tub and cannot afford to redo all the plumbing back to the stack.