Thanks for the reply sxturbo.
Ok, thanks, wlll avoid the Durgo valve route (although note that even Options A and B may require an external Durgo, since close to velux windows - I hope that is less problematic...)
Re going out the side of the wall - good idea, but unfortunately this doesn't...
First time poster with limited plumbing experience - go easy on me :)
We're doing a loft extension, and will have an internal soil stack serving a ground floor, first floor, and loft toilet - the 3 toilets are pretty well aligned. The soil stack will be 'boxed in' on the ground floor and first...