chicken with poopy but and tips of crown are white

I have an adult hen who's butt gets poop build up sometimes too. I just trim back her butt feathers, and get as much poop off her as possible by using warm water.

If you are talking about a chick, a lot of times chicks get poop build up on their butts as well. It is also sometimes called "pasty butt". Check your chicks everyday for poopy butt and remove it using warm water, and a paper towel. After your chicks are about one week of age, pasty butt is usually no longer an issue.

Good luck with your bird, and welcome to BYC!