How do you find out if the (plumbing) vent pipe that goes through the roof is blocked?
Check the pipe above the ceiling to see if the vent pipe runs horizontaly for any distance. If it does put a level on it and make sure it does not have back fall. The pipe should run downhill from the roof penetration to the point where it goes down into the wall to serve the fixtures. If it does not have back fall take a garden house on the roof if possible and look into the vent stubbed out of your roof. if you can’t visibly see a blockage spray the garden house directly into the pipe. It should take a full stream of water without backing up.
