This one may require an asprin
House built in 1940 with full bathroom on 1st floor. By your descriptions this is a wet vent system. It appears many years ago the 2nd floor bathroom (toilet, sink and closet where the tub would go) was added. I'm in the middle of gutting the 2nd floor bath to update it and add a tiled shower. I see now that the toilet and sink drain into the vent stack. Aside from moving a door and converting it into a walk-in closet, what can I do? I'm guessing I have to find a way to drop another 3" pipe to the basement to connect the toilet shower and sink.