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Our upstairs bathroom has a toilet, tub and sink. The sink drains very quickly, but starting a couple of seconds after it empties there is a gurgling sound (blub blub blub...) that lasts several seconds. I can even feel it when I hold the pipe below the sink. Consider these facts:

  1. The tub does not gurgle after it drains and the toilet does not gurgle after it is flushed (I tested by shutting off the supply before flushing so the refill noise wouldn't interfere).

  2. Two separate plumbers have snaked the sink line and declared it clear.

  3. Someone went onto the roof to run water through the vent pipe and it appeared clear.

  4. One of the plumbers went on the roof to snake the vent pipe. It went all the way down to where it met water when we ran the sink. There was no blockage found. When I look at the roof, I see two vent pipes, one with a narrower diameter - I think the plumber may have said that was just for the sink.

Despite the above, the gurgling persists. The plumbers have no explanation but they both told me that it's nothing to worry about.

I'd be interested in any opinions about what may be causing the noise and whether based on your similar experience it needs addressing with something not already done. Could this have anything to do with the underground sewer pipe? If so, why would only one plumbing fixture be affected?

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It is nothing to be worried about, the vent that prevents the tub and toilet gurgling is probably down stream from the sink. When the sink drains it blocks the vent and creates the vacuum that sucks air from the sink trap (the glug glug you hear) there are ways to reduce or possibly eliminate the noise by adding an air admittance valve under the sink counter but these can cause problems if not properly installed or if they get gunk in them. So if you want to eliminate the noise look up air admittance valve (there are some answers here that even have photos) The noise won’t hurt anything and doesn’t have anything to do with the pipe in the ground , just the vent, if you allow the sink to drain slowly it won’t make the noise in most cases.

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  • That's reassuring, thanks. As I'm not easily picturing it, can you link to a diagram that might illustrate such a configuration of vents? – Not_Einstein Mar 7 at 15:05
  • Trying to find a specific vent configuration would take a while , think of it this way, most of the time the toilet drain has the vent and other drains dump into that line. With your sink being higher and draining down to this line it is full of water for a few feet and draining fast this creates the vacuum that pulls the air through the trap. If you slow the flow from the sink by not opening the drain it may not gurgle it all depends on if the line has a slope. No slope more chance for gurgle a little slope and slower drain no gurgle, but in both cases adding an air admittance valve can fix. – Ed Beal Mar 7 at 15:19

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