Proper rest bend vs 90 degree bend with concrete

[WWilts]

Builder inclined to make do with 90-ish degree bend at bottom of soil stack from first floor WC/shower. Supported / encased in concrete (lean mix I think).

 

Is a proper rest bend with foot absolutely necessary in this case?

[markc]

4 minutes ago, WWilts said:

Builder inclined to make do with 90-ish degree bend at bottom of soil stack from first floor WC/shower. Supported / encased in concrete (lean mix I think).

 

Is a proper rest bend with foot absolutely necessary in this case?

The foot stops the bend from rolling/sliding downwards. If properly supported and prevented from moving with concrete then no problem

[WWilts]

Does the radius of the bend make a difference? Currently fairly short radius bend put in at what will be the bottom of a stack.

[markc]

Small radius is ok, I wouldn’t use an elbow at the bottom of the stack to reduce hammer. As long as it’s a bend it will stay clear