Hi, I recently picked up a couple 5 gallon carboys from a garage sale ($15 bucks each), made in Italy, typical of the ones I normally buy new from my local brew shop. One was pretty clean, the other not so clean. The guy used them for making beer so the inside of the one has a film on the inside. I soaped, soaked, scrubbed with a carboy brush and used a paddle on the end of my drill but still not as clean as I'd like. Does anyone know of a solution I can use that will dissolve this film? Thanks.