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I am adding a shower waste to my bath waste pipe and seek opinion on how I proceed. The individual wastes are approx 4/5 feet and then are to join the existing waste which runs to the stack pipe. Putting another boss on the stack pipe is not easily done. To avoid any possibility of back-flow I was considering fitting a Mcalpine Non Return Coupling to the shower waste and and also a Floplast AAV Valve.

Having researched answers in the Forum I noted there was a recommendation to put HepvO fitments on each waste pipe to prevent vacuum syphonage. It also appears ideal to prevent any possibility of waste bath water backing to the shower.

Any assistance or opinion on the fittings would be gratefully received.

dchopp,
The simpler you make the system the less likely it is to give you problems. Fit standard traps to the bath and shower and fit an AAV on the pipe from the bath near to the bath.
end

Thank you stoneyboy for your help and I am keen to avoid doing anything to impede the flow of water. However I am also keen to avoid any chance of the water from the bath waste flowing into the shower and would prefer to fit a back-flow preventer during installation. Perhaps I am worrying unduly but I am guided by the responses I have seen on the Forum. Also I intended running the bath waste pipe under the length of the bath so am possibly limited where I can site the AAV.

Would you or anybody have any further thoughts on this. Thanks

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