In my experience the Mark II removes the Krausen ring with ease as long as a little pbw is used I literally haven't used a carboy brush in years. I also clean the carboy right after I bottle and don't let it sit either.The Mark II mentioned here is good, but it won’t work for stuck-on crap IME. For krausen rings and such, I use the Clean Bottle Express. It’s a rod with chamois brushes at the end. You stick it on a drill and go to town on your carboy, kegs, whatever.
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