Gurgling sink

[Mike Barnes]

A gurgling sink - not one of life's greatest problems, but why? And what can be done to stop it? Sink empties, two seconds delay, gurgle gurgle gurgle.

It's a one-and-a-half sink with three outlets, and there is one tee, two bottle traps (BBB), and one swept tee:

Draining board Main sink Half sink | | | \________________| | | | BBB___ ___BBB BBB | | BBB . . BBB | | BBB . . .___ | # # \| # # | # EXTERNAL # |____________________________ | # WALL # | # # | . . | . . |

The pipe ends about 6" above a grid in a 12" deep well, not airtight. The gurgle comes from the main sink.

Any ideas?

And while I'm on the subject of slightly annoying but not life threatening kitchen sink problems, how do you stop a mixer tap from emptying its tube after you've turned the water off?

[Nightjar]

I would look to see if the outside gully is emptying properly. Water coming up above the end of the pipe caused a similar problem with a friend's sink.

Colin Bignell

[dom]

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[Mike Barnes]

I should have said, I already checked that.

[Mike Barnes]

Unfortunately I'm not familiar with the regs. The pipes under the sink down to the final merge are as tight as they reasonably could be. From there it's about 40 cm down and 80 cm across to the end, which doesn't seem very long to me. The route is rather tortuous, though, with four elbows. Pipe is 1-3/4" OD.

I could shorten and simplify the run by going straight out through the wall and diagonally to the drain, but that would be rather more work than I was hoping for. :-(

For a vent, what size of tube are we talking about, and where would it start from?

[Dave Liquorice]

Note that it's the working diameter of the pipe that is important not the nominal size. Is it clogged up with crud/fat etc...

The gurgle is due to the pipe filling with water and drawing air in as it flows down the pipe.

[Andrew Gabriel]

Replace one of the bottle traps with one with an integral AAV.

but check for gully emptying properly, particularly if this is a new issue that has not always happened.

[dom]

The problem is about a solid "plug" of water travelling down the pipe and sucking air through the trap. So do go with the others advice here about clear pipes and making sure your outlet is good.

I'd also forgotten about sink traps with integral vents. Another option is those HepVO things - a straight-through pipe that replaces the trap, but has a membrane that closes after fluids have passed through (never tried one - but seen warnings on here that they can eventually get partially stuck open with crud).

A vent pipe doesn't need to be full diameter, it should only be passing air. Starts from as close to the trap as you can.

But as the pipe runs are short (I think building regs says 3m for

32mm, 4m for 40mm - but don't quote me on that) - maybe it's another problem.

As others have said - has it always been like this - or has it got worse?

[Mike Barnes]

" [e-mail]" :

Thanks for that - all good stuff.

It's been installed about ten years. I really don't know whether it's always been like that, because it's one of those noises that I just block out, but occasionally it starts being noticeable again. A few years ago I had a go at it and discovered that the outside drain was blocked and the outlet pipe was under water. However when I cleared it, the problem remained. So I poured lots of boiling water down there, with no effect, shrugged, and moved on.

I'm wondering whether there might be insufficient drop, or worse, in the horizontal runs. Hard to establish because they're behind the kitchen units and in the wall. Would that explain it?