We continue to struggle to find the logic which governed the laying of the original drains. They don't seem to have been planned so much as slapped into the earth when they were needed; the plumbing makes about the same level of sense, too. The current idea is for work on the downstairs toilet to continue (indoors) while the outside walls are being built, but that may require some (further) level of replumbing first. We have tiles and a toilet, and the rest of the bathroom fixtures are on order and should be delivered soon (I hope).
Memo to self: do not leave stuff which may not deal well with being coated in dust in the hall at present (there is much chiselling of brickwork going on, to run pipes).
Updated photo gallery here.