I have a bathtub in an upstairs master bathroom. I recently noticed (couple weeks ago) that when I go to drain the tub it starts draining like normal but then after about 5 seconds it slows down dramatically. While it's draining slowly there will be an occasional sound like a big gulp of air was taken. What could cause this and how could I try fixing it?

The plumbing is about 20 years old, made from PVC. It's connected to a septic. There are two sinks nearby and a shower as well. I'm not positive if the shower shares the same drain pipes but I think they do. The only other issue I've had is that recently my kitchen island sink was burping when the dishwasher was draining. It has since stopped doing that though.

I should also note that directly beneath the tub is the laundry room.

  • 2
    The air gulp hints at a venting problem. Have you been on the roof to look for bird or insect nests, leaves, etc?
    – isherwood
    Commented Oct 30, 2018 at 13:59
  • @isherwood I have looked at the two vents on my roof and they don't seem to be covered/clogged with anything from the top. Would it be ok if I poured draino in the vent to try and clear anything out?
    – Programmer
    Commented Oct 30, 2018 at 14:02
  • I'd start with some water. Run a hose for a bit, but have someone watch inside for flooding. It should drain normally.
    – isherwood
    Commented Oct 30, 2018 at 14:05
  • @isherwood would the flooding come from a sink? Not sure where to watch for the flooding.
    – Programmer
    Commented Oct 30, 2018 at 14:05
  • Who knows? Depends on what's clogged and how it's plumbed.
    – isherwood
    Commented Oct 30, 2018 at 14:14

1 Answer 1


Sounds like the kitchen sink line has a 'fat berg', albeit a mini one. If the water is backing up along the sink line it could easily affect other connected pipework i.e. the base of the vent stack etc. I'd be tempted to start at the kitchen sink anyway as it's very often the cause of problems due to the gunk which goes down it. Hot greasy stuff goes into the sink, but as soon as it hits the cold pipes a few metres away it solidifies and builds up; often where the pipes head outside.

Grab yourself a spiral drain cleaner and remove the trap under the sink and gently clear out the run away from the sink. Finish off with a chemical cleaner if you like and plenty of hot water to flush away any remaining debris.

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