Steam cleaning is the answer

First use a tap to draw off the water, which is heavier than the diesel and should stay at the bottom of the tank. Decant the diesel into cans for the waste oil tank at the marina. Then contact all the industrial steam cleaners in your area and hope one is available in the next month… or as PBO’s Pat Manley successfully demonstrated, use a steam wallpaper stripper. (For the full version see PBO 416 – August 2001 – p46)