Can anyone explain why there's the blanket requirement that these are fitted above the flood plain of the highest device?
I've got a short SVP (strictly I guess it's a sub-stack) with a Durgo on it. Feeding the stack are a shower, bidet, WC and basin and I want to set the top of the Durgo to be just below the basin to get a flat tiled surface. If the stack gets blocked there will be an unpleasant overflowing at the loo, bidet and shower long before the basin gets affected so why do the rules say the Durgo should be above the basin overflow?