Good that they are creating disposal points although I would argue about the fact that they are needed for grey water as I see no problem in running it onto a grass verge or drain.
It was the same on Arran last summer. There are notices up on the toilets in the north not to empty toilets in the remote toilets as it screws up the sewage system but they have provided two proper disposal points unfortunately at the other end of the island but I think the loos in the main Town Brodick are ok.
I thought when I first came across the notices which were just stuck on the toilet wall on a4 paper that it was maybe campsite owners or those against wild campers that had put them up but apparently not. Its a real issue.