I asked about which acid is used in The Works because if it is not phosphoric, it will clean, but will leave the metal absolutely bare, hense vulnerable to immediate, flash rusting. Phosphoric acid will leave behind a coating (iron phosphate?) to protect the metal against rusting. Three years ago I purchased a POR-15 kit, which has three parts, Marine Clean to clean and degrease, phosphoric acid to remove rust, and the liner to seal the tank. After the first two steps (Marine Clean and phosphoric acid) the tank interior looked brand new. I elected to skip the liner and the tank interior remains the same today.