I have just in the process of replacing my bathroom. The bath and sink
wastes join up directly below the sink before exiting through the wall.
When emptying the bath the sink 'gurgles', is this syphoning? How can I
stop it, I cannot put a anti syphon trap under the bath due to space
restrictions. The old bath and sink used the exact same setup and this
didn't happen before. The only major differences now are the bath is larger
(P shaped shower bath), the bath plug is one of those spring loaded 'push to
seal, push to open' jobbies and the sink is a 'pop up' plug. Both plugs
before were regular plugs and chains.
The problem is the water from the bath is pulling a partial vacuum as
it descends down the pipe. This causes the sink waste trap to let air
in, hence the gurgling.
You need to fit an anti vac valve onto the pipe between the bath and
sink. It doesn't have to be on the bath itself.
Presumably something like this then? http://www.wickes.co.uk/invt/424903 .
Can these be fitted vertically or do they have to be horizontal to stop
leaks, as it would be easier to fit it on the sink down pipe?
I think that something like a Marley Monitor anti-syphon bottle trap,
fixed to the *sink*, will fix the problem. As the bath empties, it pulls
air from the pipe going to the sink, creating a partial vacuum which
then partially empties the sink trap and draws air into it. The
anti-syphon trap will allow air to be drawn directly into the pipe,
preventing the partial vacuum from forming.
But IANA plumber...
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