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.