Abstract: A method utilizing a portable hydraulic apparatus for cleaning the hydrocarbon contaminated sludge deposit of an oil storage tank with a fluidizing agent, the tank having a floor, a side wall and a passageway through the side wall positioned adjacent the floor of the tank, comprises a frame having a central portion and first and second end portions. The frame is configured and dimensioned to pass through the passageway. A pair of independently movable endless chain belts are position on opposite sides of the frame for selectively moving the frame within the oil storage tank to selected locations. A hydraulic line coupled to the central portion of the frame discharges the fluidizing agent onto an adjacent first portion of the sludge deposit so as to form a pool of sludge and fluidizing agent. A suction pump is positioned on the central portion of the frame for drawing up the pool of sludge and fluidizing agent.