snip
We need a description of the stuff that is blocking the drain.
Washing machine powder has been mentioned that clogs the pipes with a
hard but crumbly residue. Fat is fat thick softish stuff with not
much texture.
snip

That's ie:
Washing machine powder has been mentioned that clogs the pipes with a
*****hard but crumbly residue*****

though it's definately from the dishwasher.