My fermentation vessel of choice is the Better Bottle, a PET plastic carboy. I have several 5 and 6 gallon versions of this product and I've been very pleased. After losing a batch of beer today I noticed that the BB I'd fermented in had scratches around the top of the carboy from my carboy brush. While I don't believe this was the sole cause of the bad beer I can't rule it out as a possibility. It occurred to me that perhaps these plastic carboys need a special brush (seeing as my regular ol' carboy brush had done me a disservice), so I went to the BB website looking for a info on special cleaning equipment. As it turns out they recommend against using stiff brushes and suggest that the best method of cleaning is simply to rinse/wash/sanitize with no mechanical scrubbing. Here's a link to the washing/care instructions. I'm afraid I may have ruined this carboy, oh well- live and learn.