DesertGirl, I wanted to add:
My DH is the butt cleaner around here!
He does it this way: he fills a bowl with warm water, (test it on your wrist). He then holds the chick in his hand, gently and firmly, and moistens his fingers in the water. He then works gently at the poop with his fingers, until gradually it softens and he can remove pieces. This seems to reduce the friction on their wee bums, that may occur from vigorous wiping or rubbing.
It has been successful each time, and the poop comes off. Another technique, though not tried by us, is to hold the chick bum under the tap. You want a warm temp for tap water under a gentle stream to soften that way. My DH is tall, and thought that the angle would be too awkward for him to work at it. Hope that helps.
Persevere, it can be done. They seem to grow out of it quickly, in my experience...
For the record, my chicks receive the following: ACV in their water (search on BYC for amounts...for your waterer's capacity), chick starter crumbles, chick grit (the smallest type) and warmth...for 1 week olds I went to an even 90 degrees, with cooler spots away from the lamp. The butts all cleared up after the single treatments...