Abstract: Liquid hydrocarbon storage tanks are cleaned by transferring the most contaminated lower fuel layer to an external vessel on a treatment truck where separation into a contaminants portion and a fuel portion occurs. The remnant fuel in the storage tank is cleaned by multiple passes through an external circuit on the truck. The fuel from the vessel is sometimes returned to the remnant fuel to be cleaned. The contaminants are discarded. The initial separation shortens the cleaning cycle. A flexible dip tube stiffened by a guide rod allows probing of the storage tank floor.