I want to put a bathroom in a small attic room but the floor has only 6" studs...not 12". A structural engineer has looked at it and said that the weight isn't a problem. The problem will be the toilet. I have looked at back flush/pump assist toilets and would welcome any comments or suggestions. thanks
Why can't you drop the waste line below the 6" floor joists?
You can fir around the pipe in the ceiling.
If you don't want horizontal pipes in the floor joists,
You can also use a rear outlet floor mounted toilet
or a Wall hung toilet.
Most of these are pressure assist bowls.
More information here