I ferment exclusively in PET plastic "Better Bottle" 6 gallon carboys.
As many of you realize plastic carboys should not be cleaned with a carboy brush to avoid scratching the plastic which can lead to bacteria harboring.
Well, last night after I had trouble with some stubborn deposits from the Krausen on my carboy, even after a 24 hour Oxyclean soak I had brilliant idea. I'm sure this has been discovered before but I could not find many threads on this site on how to properly clean a plastic carboy.
How to Clean a Plastic Carboy
1. fill the carboy to the brim with a water solution with a cleaning product like Oxyclean. Soak the carboy for at least 12 hours.
2. Dump out all but about 1 gallon of the water.
3. Insert a CLEAN cotton terry rag (8x8" or 10x10" works great).
4. Plug the mouth of the carboy with your hand or another rag.
5. Lift the carboy, and hold on each end with both hands.
6. Shake the carboy violently for 2-3 minutes! It helps if you change the direction of shaking frequently to be sure the cotton rag cleans all surfaces within.
7. Invert carboy, grab the rag with your fingers or pliers and pull out of carboy
8. Rinse as usual
This worked awesome on my Better Bottle and a truly clean cotton terry towel will not scratch plastic.