Well this is a v-e-r-y messy business

So far Ginger has walked through it, then into his litter box so we had tuna/milk/litter-y paws, then walked through his bedding, then tried (repeatedly) to climb out of his tub so the walls are now semi-coated in fish/milk mix
I've put some on my finger and offered it - Ginger sniffed then snapped his head to the side like I was offering something vulgar, Meow sniffed then licked - progress! - then I popped her in front of the bowl and she lapped at the fishy milk and seemed to enjoy that - the mushy tuna is still there so hoping she'll progress to that. Gave Ginger a bottle of milk as he was fretting, poor boy and I love feeding him 
Have tidied the tub/bedding/litter ready for the next round and now all snuggled up down my top asleep :)