So far every answer by Duck-Duck-Goose has almost killed me XD
Perhaps he bathes like otters and some other animals do? Obviously they don't actually use soap but they wash in a river in a manner similar to people
Or perhaps it's like primates in that they don't really "wash" as such but kinda brush out dirt and parasites or whatever
It's a good question though :3
What book was it where Cassie gave him stuff for fleas? I don't remember that one XD