[Merlina]

Have you tried putting a pot of sand close to the wheel? It worked with mine and he peed in his wheel all night. He was fine using is toilet tray any other time but would not leave the wheel once he was running. He would poo in there too so by morning there was a lovely sticky mess coated all over. He would not take a few minutes out of his running time to visit his toilet in the far corner of his cage but he will jump out for the shorter time it takes to use the sand next to his wheel. It took him a few weeks to work out that pee, poo and sandy paws were not so comfortable for running on and now his wheel is clean most of the time.