This whole problem was caused by a blocked grey water drain system. The toilets are drained by a vacuum system into a toilet tank. This was working normally.
The toilet sink, galley sink, and bev maker overflow drain all join up and drain through the overboard drain mast. Also draining into this line is drains from the passenger door sills, and the toilet compartment floor, and the galley chillers.
The drain mast was blocked. Water poured down the toilet sink will travel through the drain line, and come out somewhere. Usually the drain by the door, or in this case the galley chiller drain. On its way through the drain system, it will pick up coffee residue and gunge that is lying in there and when it comes out it usually smells bad. (all drain lines are coated by dried coffee) This smelly water was interpreted as poo by someone, but it has nothing to do with what goes down the toilet bowl.
I Have had the same discussion with a B767 crew, and they would not believe me that the toilet system was not leaking, and it was a blocked drain.