View attachment 38226 View attachment 38227
Latest:
1) AAV added to 4 in pipe behind wall.
Building Control may allow a AAAV valve to be installed behind the WC in the void so long as it is above the overspill level of the pan & accessible.
2) Bath (with waterless trap) connects to toilet's 4 in behind wall with boss connector (see link below). May connect at exactly half line due to slope. Problem?
May be OK but would need to see in relation to pan outlet. Can't you run it further along the void before connecting?
3) Waterless trap on bath and one on each basin (or one shared)
I would definitely fit one to the bath, as this is the problem appliance.
4) Normal trap under shower (no access)
If this is to remain a water filled trap don't connect the bath waste to it as it will pull the shower trap when it is discharged.
5) 40mm AAV on the way out of both basins (confirm location-diagram)
Questions :
1) For two basins, should I install one waterless trap on each, or can they share one after a tee? (the tee can be the AAV?)
A cross tee is not a common fitting so I would have a vertical pipe in either of the corners of the vanity unit with a 40mm tee & an access on the vertical end with a 40mm float (see below) running across with 40mm tees with a 40x32mm reducer picking up each basin. You could either have normal P traps on each & off the end of the float have a vertical rise to get you up as high as you can within the unit & put a mini AAAV to allow air in & break any siphonage that may occur. The other option is just fit a 40mm waterless trap on the vertical drop in the corner.
2) If using waterless traps, the syphoning may not be a problem any more. If joining bath waste to 4 in pipe too close to toilet is a concern, can the bath waste return to the original path and join the shower pipe?
Not recommended see above
3) Don't know what a 40mm float is.
Horizontal run of pipe connecting appliances in a line, as in your basins.
Here's the shopping list so far : Please recommend alternatives if these are bad for any reason.
110mm AAV (Durgo) : https://www.NoLinkingToThis/p/floplast-ax110g-air-admittance-valve-grey/47962
40mm AAV for basin: https://www.NoLinkingToThis/p/floplast-af32w-air-admittance-valve/42968
Boss Connector :
Water Waste BIG BOSS Pipe Adaptor - 40mm - 1.1/2"- Black - Pipe & Fittings | BES.co.uk-19871 | BES.co.uk
I don't like these & would always try to use a 110mm boss pipe to connect waste to soil pipe, if not possible then a strap-on but these (IMHO) are fine for connecting a condensate waste to an existing stack externally but lack the strength effect the bore.
Waterless trap: https://www.NoLinkingToThis/p/osma-waste-valve-white-x/1819K
Don't forget you will need the adapters for one end if you are not going straight onto an appliance.