Goodness, Prime is a cutie! Are the bigger chicks being good to him?
There definitely is lots of info on pasty butt, but I'll tell ya, I have found that it clears up quickest by trimming the few little feathers that catch the poo, and even more by gently working the poop off dry, without washing. It may make it a little raw, but after watching a broody hen rip it off a chick, I thought "she can't wash it". So I've tried it dry on other chicks, and it seems to only take a couple of times that way, and it's gone. Maybe coincidence, but figured I'd throw it out there.
Thanks for the Prime update!