https://www.backyardchickens.com/t/884172/sick-rir-weight-loss-green-runny-poop-now-fly-strike-graphic-pics/10
Couldn't remember if I had posted the pics or not - see post #12 in the above thread.
I washed the area with warm water which removed a lot of them, them spent at least an hour...
I unfortunately dealt with fly strike once when a chicken of mine had a poopy butt for too long. Next thing I know, the strike turned into a giant mass of maggots. Stomach turning.
I would be happy to post a pic if you're interested but it's NSFW to be sure.