It also pongs something terrible in hot weather so I'd at least try to move
the first elbow so its uphill not downhill of the other bend.
Brian

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The Sofa of Brian Gaff...

Blind user, so no pictures please!
"NY" wrote in message
o.uk...
Our bath/washbasin waste pipe emerges through the wall and then, via an
elbow, goes very slightly *uphill* for a run of a couple of feet, before
another elbow joint connects to a vertical pipe to ground level. The
highest point is probably an inch or so above the point where the pipe
emerges through the house wall, but as far as I can estimate, is below the
level of the bath plughole.

Is this likely to be responsible for water that is run out of the bath
ejecting the water from the washbasin U trap, or water from the washbasin
flowing into the bath and/or ejecting the bath's U trap wate, with copious
gurgling? And also causing very slow drainage of water from the bath
(several minutes to empty the bath).

I can see that even if it's not the cause of the gurgling and back flow
into the bath, it's not a good idea to have water standing in the pipe
because it will (and does!) freeze in cold weather: several times I've had
to dismantle the pipework and pour boiling water down the section that is
normally horizontal/uphill, to encourage the plug of ice to emerge.