Re: bath wastes sizes
if you cant get you r tolerances on a single stack system then you need to adjust to single stack modified!
The problem i see with durgos (although i do use them when i have to ) is that not inly do you need air to enter the system but also exit!! a durgo has non return so how can air escape if need be to give an equal positive nad negative pressure in the pipe work??
I can t see the main stack vent doing this as although it is 4" to the termination its axillary purpose is to vent the manhole hence such a large termination. Most fixture unit rating on a domestic property could really se you use a 50mm stack vent but venting the manhole prevents this!
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