use paper towels to convince as much of it off as possible, then run lukewarm water over their bum carefully to not soak them too much. Then you can try to work some more of it off w/ towels. BUT I did go ahead and pull some of the fluff off those that had it the worst. It seems to have helped to not have so much fluff near the vent and it has not been back since. Just it should be done carefully, I pulled some mud/poop off my hen this past week near her vent thinking quick and easy, poor critter had a small wound from where the feather ripped out. I felt so bad.
