This is going to be a wet room, shower one side, loo and basin the other, underfloor heating to keep it dry.
Stage 1 was to set the ACO drain in place.
on top of the concrete will be 50mm celotex, UFH pipe and 75mm of fibre reinforced screed.
We used some beefy brackets from Screwfix, then some M10 bolts plus locking nuts to set the ACO drain some 12mm below the screed height of the adjoining lobby floor.
We will lay the screed level in the entrance (so it marries to the doorway correctly), then slopes 12mm over 600mm to this drain. Floor in shower will slope back towards same drain.
Drain was fiddly - but got it right after many dry fits followed but solvent welding. As recommended, we wrapped the bottle trap in foam and put some thin foam (pipe insulation split open) around the pipes, so they will be able to move and expand slightly rather than be solidly buried in concrete and screed.
Ideally the pipe would go down under the ACO strip, but the builders installed off to one side as it was convenient to intercept the 110 pipe below that takes the grey water from the kitchen and bathroom.
However, there'll be plenty of screed over this, so it will be solid enough.
Tested the drain and flow is excellent :)
To be continued....