Abstract: A cleaning adapter apparatus comprises a swivel support device adapted to be sealed over a wall aperture in the lower portion of the tank wall. A swiveling body defines a cleaning channel therethrough and is sealed in the swivel support device such that the swiveling body can move horizontally with an outer end of the cleaning channel exposed on an outside of the tank, and an inner end exposed on an inside of the tank. A valve is connected to the outer end of the cleaning channel and is adapted for connection to a vacuum tube and internal pressure wand of a vacuum truck such that the pressure wand can pass through the valve and cleaning channel into the tank. The pressure wand can be moved from side to side in addition to in and out while cleaning the tank with the method of the invention.