As suggested - 3 reasons it's not ideal to do the complete run in 40mm
1) overall length of the run, as mentioned, if it's over 3m then you need to step it up at least 1 size if abiding by the regs
2) running any waste vertically then the falling waste water needs air space to ensure it doesn't create a vacuum otherwise you would need to vent the head of the run to avoid self syphonage at the trap(s).
3) excess noise from the falling water in a confined space
1) overall length of the run, as mentioned, if it's over 3m then you need to step it up at least 1 size if abiding by the regs
2) running any waste vertically then the falling waste water needs air space to ensure it doesn't create a vacuum otherwise you would need to vent the head of the run to avoid self syphonage at the trap(s).
3) excess noise from the falling water in a confined space
