A hot tank is an industrial method for stripping paint, grease, rust and other undesirables from metal components. Essentially, the part is lowered into a heated and agitated vat of a corrosive substance designed to remove the aforementioned without damaging the metal of the part. Typically used to prepare auto parts for painting or restoration. Really a huge parts washer. The EPA makes these expensive to operate. Hot-tanking is the verb describing the act of running a part through a hot tank.