There are so many different types of brushes out there, some people swear by the furminator, they are a bit more pricey and I think they can be too much for longer coats like that of a lionhead, but are good for shorter fur.
I've also had recommended to me a simple black men's comb with fine bristles and apparently they work well, though I haven't tried it yet myself.
Bunnylovin is correct in saying that your nethie shouldn't be having poopy butt. I would take a good look at his diet and would probably begin by cutting it back to just hay and his daily serve of pellets. If that doesn't work, reduce the amount of pellets. What serving size of pellets does he get every day?