Peter Scott wrote:
wrote in message
oups.com...


Screwfix and local hardware shop don't seem to have non-return valves
to fit in line.

You can definitely get them (Or could; I once bought one from B&Q years
ago for this purpose). I suspect most modern washers/dishwashers have
them built-in now though - worth checking yours in case you're
misdiagnosing it!

The problem is syphonage. To stop it you have to provide a way for air to
get in to each of the waste pipes. The usual way is to have a vertical piece
of plastic waste pipe. This has a u-trap at the bottom and is open at the
top. You can buy them readymade at merchants. You then poke the end of the
waste pipe from the dw into it. Its a good idea to secure it perhaps with a
cup-hook in the wall onto which you push the hole you normally get on the
crook in the waste pipe. Never happened to me but I'm told that the pipes
can jump out. Yuk! Do the same with the wash machine. Hey presto, no
syphoning. BTW best not to run the machines at the same time. A long waste
pipe can be overloaded and back up. Again yuk! This gets worse after a year
or two when the pipe starts to get clagged up.

Alternatively anti-syphon valves are also (or were!) available from B&Q
- you fit them at the highest point of the waste and they let air in
through a valve. Peter's solution is a lot better, but mine is a lot
quicker if it does the trick!

David