Strange deposits

I went to clean out the buns litter tray this morning, and on top of my girls wee (which is red) and on top of some poo (not sure if girls or boys poo) is this like weird paste stuff. Its pinky colour and like the consistency of panacur (they haven't had any recently) any ideas?

sounds like calcium sludge maybe.....bunnys excrete any calcium not needed in their pee (which you said was quite highly coloured). If they are eating too much calcium their wee can become almost toothpaste like.

One easy way to test is to let it dry & then pour vinagar on it.....if it fizzes it is probably calcium sludge. If it doesn't I have no idea.