Combined bath/shower wastes

[Adrian_P]

Hi. If I want to connect bath and shower wastes so they come out of the same pipe to the soil stack, what size does it have to be? 50mm?
I've read that I need and anti-syphon valve too, as the shower waste run will be over 2 meters, under the bath. Do the bath and shower wastes have to be 40mm or 32, before joining the 50mm? Thanks

 

[Deleted member 120897]

Minimum size should match the trap, if it’s unventilated then the size can vary. Building regulations document H gives guidance.