From what I remember the soil pipe (blue) went something like this to go from the toilet at the front to the existing soil pipe at the back. The little step (red) just allowed it to start with a bit of extra height to get the drop.
Ahhhh really interesting, I couldn't get my head round how people put bathrooms by stairs. Do you know how they got the soil pipe through the steels? Your place looks like an awesome layout too, hate to be dad head but the octagon room would make such a cool kids space.
Cheers for sharing! I'm defo a bit confused! Dont suppose you have a floor plan?
This is what I ma thinking for mine, and avoiding a macerator... is this madness?