Washing machine/Dishwasher drain

15 Jan 2007
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United Kingdom

We have a dishwasher and washing machine next to each other in the kitchen. The dishwasher drain is via a 'standard' trap and stand pipe to the outside drain, the washing machine drains via a spigot attachment to the trap on the sink waste.

Everything works ok except that we get horrible 'bad drains smells' in the kitchen whenever the washing machine is running.

So, couple of questions - is there anything inherently wrong with the setup we have at present that would cause the bad odour? secondly, is there any way of connecting the washing machine via the dishwasher drain (doubling up the drains into the one standpipe?). I have looked outside and due to the presence of a drain pipe from the kitchen roof there doesn't seem to be any room to fit a second stand alone drain for the washer.

Any suggestions appreciated, thanks
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does the washer waste enter the waste pipe above or below the trap?

Just checked - it enters above the trap. Is this significant? because looking in the screwfix catalogue all of the sink traps that have a washing machine inlet seem to enter above the trap.
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If it was below the trap it would be acting like a vent pipe for the drain... but then you'd get the smells all the time.
I'm guessing that the waste from your washer is the type where the washer outlet hose fixes directly to a kind push fitting that stands off the waste pipe?
If so the smell can only be coming from the dishwasher waste pipe and my guess is that as the washer discharges it's pushing the water through the u-bend so fast that it's partially clearing the water out of the trap and allowing air and smell to pass back through from your drains?
Just a guess without a picture and some rough measurements it's hard to say more.

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