Bath waste coming up in shower tray


4 May 2005
Reaction score
United Kingdom
I have my bath and shower on the same waste run. When the bath is emptied from full, due to the head of water above the shower tray level, some bath water bubbles up into the shower tray.
I was going to fit an inline oneway valve to the shower waste run before it meets the bath waste. A plumber told me I just need to fit an anti siphon waste to the bath and this will solve the problem. Firstly how do these things work? Secondly is he correct, will this prevent the bath water running up the pipe and out into the shower tray?

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Does the bath water actually enter the shower tray? Or is it just a bubbling sound?

If the trap just bubbles then it may well be siphonage as the bath water sucks the water out of the shower trap. The anti-vauum would need to be fitted to the shower tray and not the bath.
They work by admitting air into the pipework when negative pressure is present. Basically the suction opens a little valve and lets air in preventing the water in the trap from being sucked out.

If the water is entering the shower tray then an anti-siphon/vacuum trap is not going to help you. The in-line valve may work, but I have never used them, maybe others could comment. If not then the pipe work will have to be adjusted to prevent the problem, probably with the shower and bath having dedicated wastes to the stack/gully.
Thanks Moley, the water actually comes up into the shower tray.
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I think that is probably what I need. I'll speak to the my local supplier. Thanks.
Just re-read my post :LOL:

Vale = Valve

Nice to put something back into this forum for a chx :)
I have fitted the inline non return valves both on jobs and at home to solve the same problem with the baths and showers and they work very well so I can recommend them to you. Just make sure they are fitted the right way round !

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