An apparatus for cleaning vessels is inserted into a vessel to automatically clean the interior thereof. The apparatus is particularly adapted to clean rail tank cars and similar vessels, and includes a spray nozzle that is moved at a controlled speed back and forth across the length and width of deposits within the tank to blast loose and flush the deposits out of a drain from the tank. The spray nozzle is carried at a lower end of a support trunk, and is rotated back and forth about respective longitudinal and transverse axes to direct a jet stream of solvent against the deposits. The support trunk is pivotable to shift the spray nozzle from side to side within the vessel to clean behind obstructions often found in tanks, and vertically movable to position the spray nozzle at selected heights within the tank. The apparatus can be rotated about a vertical axis to rotate the longitudinal and transverse axes about which the spray nozzle is rotated.