Stop sink overflow pipe trapping water and getting smelly

9 Jul 2008
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United Kingdom
Hi all,

I was helped on these forums to diagnose a smelly kitchen sink. It turned out that the overflow pipe was to blame.

I now periodically clean the pipe, but the smell and gunk come back. This is due to a design flaw. I am looking for advice on how to fix this.

The sink is a double sink and the overflow pipe runs in a U-shaped path between overflow inlet in the main sink and drains into the plug drain fitting for the second sink.

Because of it's U shape, it fills with water whenever the second sink is drained and collects debris. Soon this standing water becomes brackish and smelly.

A natural way to fix this would be to replumb the overflow pipe so that it drains vertically down and connects to the waste pipe which runs below it. However, I think installing an extra pipe junction on this pipe is beyond my plumbing skills. Can anyone suggest another way to avoid the overflow pipe retaining water?

I am astonished that this design is used at all, but it seems to be a common one - how can a sink overflow be designed in this way and not get standing water in the pipe?

I'm grateful for any advice or suggestions. Thanks very much.

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Whoever has fitted that has mixed up the wastes, the one your overflow is going to should be fitted to the sink not the half bowl. That way the pipe would be vertical without the unnecessary bend.
Sooey - I think you are right. Is it easy to remove and replace those sink waste fittings? I feel competent to take apart the rest of the sink pipe-work but have never removed a sink plug waste fitting.

Unfortunately, in an earlier attempt to take out the U (which didn't work), I shortened the overflow pipe, so I'll need to source a new one of those too.
Very easy, they just unscrew from above, after undoing the connections below.
Put a bowl under to catch any water in the traps.
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Hi Sooey,

I have swapped the sink wastes and all is almost well. The overflow seems in a much better configuration now, and I hope it won't accumulate waste water.

I do have a problem though with re-sealing the wastes to the sinks. When I removed them there was some black residue between the metal waste assembly and the sink. This must have been sealing the leak. It was decayed so I cleaned it away.

The sink now has a slow leak when filled. What do you recommend to seal between the waste assembly and sink? Some youtube videos have recommended putty. Is that the thing to use?

BTW Here is what the overflow looks like now. Much better!

Edit: Now everything has dried out, that "slow leak" has not reappeared. I think it was just condensation on the pipes. Very satisfying to have fixed this myself. Great forum!
There's usually a thin rubber seal between the waste assembly and the sink, if there's no seal there now you will probably find the water level in the sink drops with the plug in.
The easy way to fix that is to take it back off and run a bead of clear silicone where the seal should sit.
Thanks. Although it seems to be holding water now I don't want to create problems for the future so I'll get some sealant on.

Do you let the sealant dry in place before fitting the waste plate to the sink? Or tighten the fitting with wet sealant and then remove excess?

Why is silicone preferred to plumber's putty?
You can use plumbers mait if you like, it will do just as well..

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