I think my vent stack is plugged; I think this because the toilets sound different while flushing than I think they should, and I hear a knocking in the wall when a sink or toilet is flushed. Normally I would go up on the roof and look in the vent stack, but my roof has a steep angle and is not walkable. I realize I could use roof jacks, but I'm hoping I can avoid it.

What I would like to do is go into the attic where there is plenty of room to work and cut the vent stack into two halves so I can look in it that way (The vent stack is PVC). After checking for blocks and fixing if necessary, I would re-attach the stack with a rubber coupling meant for PVC pipe, or if that's discouraged, weld a PVC coupling to re-attach the two halves.

Would my idea be acceptable? I can't see any functional problem with it, but I'm wondering what an inspector might think years down the line, or if it's against code.

3 Answers 3


I'd suggest cutting out enough pipe to insert a cleanout tee & threaded plug, either "instead of a coupling" or "along with a rubber coupler" if you go that route due to pipe (lack of) vertical motion.

If you had to clean it out once, you might need to again. If not using a cleanout, that votes in favor of the rubber coupling, since it's removable "next time."

  • I had not thought of this, but it makes sense. The only issue I can see with this is if I put the clean out near the top of the roofline and somehow, the block next time is between that point and the top of the vent stack.
    – Carl
    Oct 1, 2020 at 11:58
  • Could I use a "T" to do this instead of a "Y"?
    – Carl
    Oct 1, 2020 at 12:12
  • 1
    A Tee is standard for exactly that reason - a cleanout tee (unlike one meant to attach a pipe to) is short on the threaded port so it's easy to rod both directions.
    – Ecnerwal
    Oct 1, 2020 at 12:32

I'd opt for the PVC coupling and certainly that's going to be less expensive than one of those rubber couplers. In most places they are acceptable but many require the kind with the metal sheath:

enter image description here

  • 1
    I agree. I've never seen anything that states a vent pipe can't have a straight coupling in it. +1
    – JACK
    Sep 30, 2020 at 18:06
  • 1
    I vote for the PVC coupler, Would a clean out fitting be allowed?
    – Alaska Man
    Sep 30, 2020 at 20:07
  • @AlaskaMan That's a good thought. In case it gets blocked again that would eliminate the need to climb on the roof or cut the pipe again.
    – jwh20
    Sep 30, 2020 at 22:17
  • 1
    PVC coupling requires having vertical motion sufficient to make the joint, unless you are brave enough to use a repair coupling (Given how quickly PVC can "grab" when cementing, I view those as a dice roll.) Your roof jack may or may not be amused when you try to move the pipe up and down, depending on specifics.
    – Ecnerwal
    Sep 30, 2020 at 22:48
  • Just to be clear, by 'roof jack' I meant a platform I can screw into the roof and stand on. bigrocksupply.com/resize/shared/images/products/…
    – Carl
    Oct 1, 2020 at 12:00

Since we're thinking outside the box.. if the rubber coupler is frowned upon, then how about a male and female adapter? This gives the on-axis access that a coupler would give while avoiding the one-time limit of a weld-on coupler and also the question of acceptability with the rubber coupler.

  • Basically, a PVC union, I like it! Oct 1, 2020 at 2:26
  • ...But rubber couplers are generally not frowned on. They are the standard modern method to join cast iron pipes, cast to PVC transitions, and are listed for PVC to PVC as well.
    – Ecnerwal
    Oct 1, 2020 at 4:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.