I get a container with warm water only-no soap, a rubber glove, scissors. Tuck the chicken under my arm backwards. (Silent prayer that chicken doesn't poop in my face while I'm cleaning.) Trim any chunky parts that won't come out easily. Then I scoop some water with my gloved hand onto the poop and gently try to work it out. It usually mostly comes off after a few times. Another for a rinse then squeeze the water out of the feathers without pulling them too much. At 45 F. I wouldn't bother drying as I try to do it with the minimal amount of wet on the chicken as possible. But a quick blow dry can also work if needed more water or I expect colder weather before they dry. Most chickens seem to like being blow dried in my experience. If chronic poopy but is happening, you may want to check diet that they're not getting to many treats, deworm or check for a crop issue these can cause this. That being said some chickens just have wetter poo for no bad reason. I've had one that's been like that since day 1 and she's a healthy happy layer. Trims and a weekly bum wash is the norm with her. A feather trim for an exceptionally fluffy butt is also an option but I wouldn't trim her bald since that can attract pecking and give her a chapped cold bum in winter. Also, If it's really caked on there you might have to soak her and work it out then blow dry.
