Not the nicest of jobs. Thankfully Willow's never looks too bad, so I leave alone.
There is a lady on our yard who never fails to amaze me. She somehow manages to get it out (sorry not very good at wording this) and she holds it. So he can't draw it back in. She uses a sheath cleaner spray and sponge. Her horse seems to like it too, I think if I tried to do that to Willow, I'd probably get a cow kick or two.
I've seen other people hold a hose there too, not sure if it works.