This is hard to explain.. But I was sitting in my bedroom when all of a sudden my toilet started draining, then the sinks in the bathroom started pulling air in, then when the water from the toilet drained, it started suctioning air down the toilet too. It all lasted about 20 to 30 seconds. This apparently happened a couple of weeks ago as well according to my wife.

This only happens in our new addition to the house, which has a partially separate line to the sewer (it joins up to the main line about 15 feet in front of the house). I didn't see any sign that it affected other parts of the house on the original waste water line.

My only guess is that the suction is coming from all of the water in the line draining into the sewer at once, pulling air with it until the sewer line is open to the air.

We have a tub, a toilet, a shower and two sinks on this line and none of them were in use at the time. I was seriously considering that someone was working on the sewer line outside with a vacuum or something. Any ideas what might be happening here?

UPDATED WITH PHOTOS: Here you can see multiple vent pipes. I snaked both the close one and the far one. Time will tell if it worked Photo of the roof above the addition, multiple vent pipes

  • 7
    Does new addition have it own vent stack?
    – crip659
    Commented Mar 31, 2021 at 22:35
  • I believe it does. We have an HVAC unit in the attic which appears to have an exhaust for the heater (I assume thats what it is since it has a series of vented holes in it and a cap), then there's a second bare looking pipe, which I would assume is for the plumbing
    – Matt
    Commented Mar 31, 2021 at 22:41
  • 9
    Almost certainly a venting issue perhaps not adequately sized or a blockage in the stack
    – Kris
    Commented Mar 31, 2021 at 22:52
  • 1
    Have someone run some water and flush the toilet and you listen up at the vent. you should be able to here the water running.
    – JACK
    Commented Mar 31, 2021 at 23:03
  • 3
    A vent stack is a plumbing pipe that allows air to enter the system it is in no way connected to HVAC, it sounds like your addition has poorly vented plumbing.
    – Jasen
    Commented Apr 1, 2021 at 6:07

4 Answers 4


Even if someone was "working on the sewer lines with a vacuum" properly sized and functional vents would keep the traps from siphoning.

So, you have vents which are not functioning as they should, whether from being built improperly in the "new addition" (since the problem is limited to there) or from some sort of blockage (animal nest in the vent pipe or the like.)

You, or, if that's not your thing, someone you hire should get up on the roof and check the vent pipe there, perhaps with a snake in hand to try cleaning it. Dumping a bucket of water down, or running water from a hose down can also sometimes be helpful in identifying a blockage (and can sometimes help to clear it.)

After that you (or someone you hire if it's not your thing) would get to checking and using all the cleanouts down inside the house, if the problem persists. For a typical venting setup with a single toilet, the fact that the toilet is affected points to the main vent (for this section of the house) being blocked, not just some tributary branch vent.

  • 50
    Before dumping a bucketfull of water in, make sure you're really looking at your drain vent and not, say, the vent from a bathroom exhaust fan.
    – TooTea
    Commented Apr 1, 2021 at 8:24
  • 16
    @TooTea that sounds like wisdom-hard-won. Good point.
    – Criggie
    Commented Apr 1, 2021 at 10:00
  • 2
    That actually made me chuckle. But I'll be cautious, thanks :)
    – Matt
    Commented Apr 1, 2021 at 16:35
  • 11
    Worth adding that this needs to be fixed ASAP or OP will end up with a house full of sewer gas (if that's not already obvious to them). It's not just an oddity that can be ignored.
    – J...
    Commented Apr 1, 2021 at 17:27
  • 2
    @TooTea If your bathroom exhaust vent is pointing straight up then, I dare say, you have bigger problems!
    – J...
    Commented Apr 1, 2021 at 18:05

Check your roof vent for obstructions (leaves, acorns, animals) by running a drain auger (snake) down the vent.

If it's clear (open) it may be an undersized vent or one that isn't located properly.


As the others say, a venting problem, and possibly your neighbours have one too. It’s as if your Neighbor upstairs lets most of the water out of the bath, and then puts the plug in. Result is partial vacuum in sewer.

  • 2
    I have a single family home, but if I lived in a duplex or multi-family building, that would certainly be a possibility. Thanks for the answer
    – Matt
    Commented Apr 1, 2021 at 16:35

We had exactly the same issue, toilet and bathtub sucking air whenever one or the other was draining. We also thought the vent stack was the problem, and opened the stack up under the roofline (as it was winter and our roof was snow-covered) to eliminate the possibility of a blockage in the vent. That didn't improve the problem. The complete fix turned out to be the removal of a clog (using a roto-rooter) about 10 meters down the drain line (almost at our property line). Once gone, no problems since.

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