I would propose a new kind of brush that helps making pipes.
Basically, you get two outlines (one blue, one red) which denote the wall thickness of your pipe.
With ctrl and shift you can change either of these outlines.
when clicking with an element selected, it will only be placed between the blue and red outline (And erased inside the red outline, which is the inner diameter).
Is this somehow obtainable? (And I hope it was not posted before.)
Hollow brushes would be cool