Soil pipe fall and bath L brackets

[Fallout]

Is the required fall for 4 inch soil pipe between 18mm and 90mm? And between 18-44mm for 1.5 and 1.25inch pipe?

Also when install a bath and using the l brackets on a stud wall and a dot and dab wall do you take the plaster/board off straight back to the wood stub or breeze wall and have the brakets extended out to sit flush back to this?
Thanks

 

[Madrab]

Yes as the regs go, 18 > 90mm for all If I remember rightly, always aim for somewhere in the middle and less for a 4" >18mm

Personally I don't use the brackets, I always use a baton along the long and short edges, either fixed to the studs or using longer screws and drill through to the wall and use plugs. Therefore no need for them.