Plumbing Question

Bowl and a half kitchen sink waste

I have separate bottle traps installed on both sinks linking individually back to the main waste pipe at the rear of the sinks, the main waste is an inch and a quarter this runs horizontally back to a main stack about 2.5mtrs from the kitchen . I have a washing machine trap installed at the end of the waste again under the sink. I have been getting smells coming up from the sinks and water backflowing into the main sink when the washing machine is in waste mode. Also when the main sink is emptying, the small sink has an amount of water backflowing into the plug hole but drains when the main sink has emptied.

6 Answers

Best Answer

Sounds like you have a few faults with the way your sink waste has been fitted!
Firstly bottle traps shouldn't ever be used on kitchen sinks, they're not designed for it as they get blocked up with food debris etc. It also sounds as though there isn't enough fall on the waste pipe (minimum 20mm per meter) your sink should also be connected to a MINIMUM inch and a half waste pipe and definately not inch and a quarter, when you empty a full bowl the pipe will be running at full bore creating a vacum behind it and sucking the water out of the other trap hence the smell coming up from the drains .
It would be best to get a plumber in to do the job properly i.e re run the waste in the correct size pipe, bin the two bottle traps, fit a purpose made bowl and a half waste kit with a single P or S TRAP and appliance connection.

Hope this helps
D2 Plumbing & Heating

Answered 21st Jun 2011

D2 Plumbing & Heating

Member since 18 May 2011

potentially i would guess there is not enough fall on one of the waste traps or pipework but also i feel eliminating the small bowl trap and changing main sink trap to accomodate you will gain a better flow of water through waste hopefully eliminating smells.

Answered 21st Jun 2011

Dec-Build Builders

Member since 10 Feb 2011

The main problem you are having, is that the main pipework back to the stack, is undersized. It should be a minimum of inch and a half pipe. Once this pipe is upgraded it should remedy the syphonage problem, which is causing the other trap/traps to loose their seals.

This is the cause of the bad smells coming back up from the drains, to remedy this problem shouldn't be too difficult, which is of course dependant on your current set up!

Answered 22nd Jun 2011

To The Point Plumbing

Member since 19 Feb 2009

I agree with what's been said but I realise you might not want to go to a lot of expense so here's a tip. Pop into a plumbers merchants and ask for a Hep valve - it's a dry trap which is easily fitted onto the pipe run before it gets to the stack.
Doesn't cure the bottle trap problem (blocking) but if you keep them clear with plenty of detergent and hot water you might be lucky.

All the best


Answered 23rd Jun 2011

Trust Plumbing Scarborough

Member since 17 Aug 2010

Is your waste level or does it have a fall built into it?
I'd fit a non return valve into the pipe any way and think about upgrading to 40mm pipe

Answered 21st Jun 2011

Foster Electrical & Property Maintenance

Member since 25 Mar 2009

Clean washing machine trap & check waste pipe into main stack. Or you could purchase a bottle of drain doctor from B&Q pour that directly into trap it should clear itself after a few minutes but. READ INSTRUCTIONS BEFORE YOU START............

Answered 21st Jun 2011

H Kirby Building services Ltd

Member since 9 May 2011

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