Okay, this is for the next chick that gets a pasty butt -
1. When they get a pastyB that could mean that they've been in the heat lamp too long (or at least thats what i've heard)
2. I don't "rip" it off, soak it, or drench in in peroxide, I simply -
A) Take 2-3 sheets of paper towel
B) Go to your sink and soak it in warm water, then squeeze it so it is just damp.
C) Go over to your chick, pick her/him up and place him in your hands.
D) Take the Damp cloth and rap it around it's rear end 
E) Hold it there for a few seconds so the poop is fairly wet.
F) Gently take two fingers and place them over the paper towel.
G) Next, while the poop is wet, squeeze it over the poop area and ever so slightly pull. 
*note*
Do this fast, not slowly and painfully!
H) Throw the paper towel away and wash your hands
I) Finally, go over to your chick and pet it, so it doesn't get scared of you. 