Purpose of vent under sink?

Jimmy8127 · Jun 30, 2024

There are bad smells that come from my sink drain when I run water.

On inspecting (undoing) the U-bend trap, there is no debris or anything in there. It is a clean run. And I don't think the water is being siphoned out of the U-bend (though I can't be certain) because the sink is used a lot and the smells occur when I run water, not when I leave it alone.

I was puzzled as to the purpose of the vent that points upward and to the left in the attached picture. It seems to be on the wrong side of the U-bend to be an air admittance valve, and I don't see how it can help at all since air is already free to enter through the sink plugholes.

On inspecting this vent (valve?), it was full of smelly gunk (second attached picture), so I think it's this that is causing the smell. Is there any reason this vent can't be eliminated, using a short section of pipe without the T-off to replace existing section?

Thanks in advance for any advice.

ShaunCorbs · Jun 30, 2024

That’s not a vent

That an outlet for a dishwasher / washing machine drain so should be capped if not being used temporarily you can cut the finger off a rubber glove and the smell should be gone

Jimmy8127 · Jun 30, 2024

Brilliant. Thank you very much.

I could see a vent made no sense but I couldn't think what it actually was, and your explanation makes perfect sense. I think the washing machine drain pipe must have been moved years ago.

(Having a little trouble saying anything here because there is an aggressive spam filter that prevents most attempts at an answer, including a simple thank you. It seems "o u t l e t" is not allowed.)

Though I don't think the glove finger would prevent the smell because it's coming up through the kitchen sink drain. I think the smell is caused by bits of food from the sink lodging in the out-let and then decaying there because there is no water flow to move them along. So I guess the solution would be to replace that 12cm or so section of pipe with just a straight down bit and no out-let(?)

ShaunCorbs · Jun 30, 2024

Jimmy8127 said:
Brilliant. Thank you very much.

I could see a vent made no sense but I couldn't think what it actually was, and your explanation makes perfect sense. I think the washing machine drain pipe must have been moved years ago.

(Having a little trouble saying anything here because there is an aggressive spam filter that prevents most attempts at an answer, including a simple thank you. It seems "o u t l e t" is not allowed.)

Though I don't think the glove finger would prevent the smell because it's coming up through the kitchen sink drain. I think the smell is caused by bits of food from the sink lodging in the out-let and then decaying there because there is no water flow to move them along. So I guess the solution would be to replace that 12cm or so section of pipe with just a straight down bit and no out-let(?)

Or just strip it and clean all the gunk out ?

Jimmy8127 · Jun 30, 2024

ShaunCorbs said:
Or just strip it and clean all the gunk out ?

That's what I'll do right now. Just thinking how to prevent the gunk building up again in the future.

ShaunCorbs · Jun 30, 2024

McAlpine Adjustable Inlet 'P' Trap

• 75mm water seal• 1½" Multifit compression outlet suits all plastic, copper and lead pipe• Adjustable inlet makes trap suitable for all domestic repair, maintenance and improvement work• Manufactured in polypropylene• Conforms to BS EN 274-1:2002

www.toolstation.com

That would replace the outlet / p trap

Jimmy8127 · Jun 30, 2024

ShaunCorbs said:
That would replace the out-let / p trap

Great, thanks. Much appreciated.

Purpose of vent under sink?

Jimmy8127

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