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Hi All We have 2 completely conflicting "recommendations" from bathroom fitters and don't know who is right: We have 3 upstairs bathrooms/toilets in our house, on 3 different sides of the property - bathroom 1 has an external soil vent whilst bathrooms 2 and 3 have internal 110mm air admittance valves coming off the toilet (both boxed in within the room). We are on a septic tank so presumably the 3 soil wastes join up somewhere underground before there. We want to modernise bathroom 2 with a freestanding bath and hence want to remove the existing boxed in soil pipe that travels 2m across the floor to a full-size AAV that is in the corner of the bathroom. As well as looking much neater, we also really need that extra width for the freestanding bath to fit comfortably: Fitter #1 says we must keep a full-size AAV and it must go 200mm above the height of the toilet/sink (can't remember which but basically about 1000mm above floor). This means we either have to keep the ugly boxed in pipes or build a false wall / conduit up into the roof space, which there isn't really space or a place for due to shower and window. Fitter #2 says it's sufficient to install a small AAV on the sink waste hidden within the sink unit and remove the soil pipe AAV completely - this means all pipework is then below floor and out of sight, and we can have a nice neat bathroom with a freestanding bath. From reading here and elsewhere online there seems to be contradictory advice on which is right. Some say you absolutely must have full size 110mm soil waste AAV at 200mm above overflow; others seem to suggest that if you can't accomodate that then a smaller 50mm is OK, and it can even be below overflow level if it's pressure-tested type A? Other advice seems to indicate that as there is an external vent elsewhere on the waste system the smaller AAV would be OK, but is that correct even on a completely different arm of the waste system? I'm really confused - any advice would be very gratefully received thanks! 🙂

I am trying to plan the stub stack for our downstairs toilet. The 110mm pipe is set in the slab and goes direct to a manhole outside. The cloakroom has a toilet and sink only. The stub Stack will be in the corner of the room. Does it have to be 110mm with a 110mm AAV or can i use say 50mm for the stack only with a 50mm AAV, allowing the stack to be hidden