An apparatus for removing formation sand from an oil storage tank. The apparatus is mounted to a truck towable trailer so that it may be transported to remote sites. Mounted to the truck towable trailer is a container adapted to accept and dewater a sand-water slurry pumped from the oil storage tank. The slurry is formed by injecting high pressure water from a water reservoir mounted to the truck towable trailer into the approximate centre of mass of the formation sand by way of a pipe having a nozzle generating a spherical spray pattern within the slurry. The pipe is forced into the slurry by way of a two counter-rotating drive wheels in frictional contact with the pipe. Included in the apparatus is a bifurcated conduit adapted for attachment to the storage tank drain port adapted for the injection of high pressure through one branch of the conduit and withdrawal of slurry from the other branch and into the container by way of a slurry pump. The dewatering of the slurry takes place by a plurality of screen filters mounted to the bottom, side and front inside walls of the container. Oil and water extracted from the slurry is recycled back into the storage tank for later removal and treatment. All pumps and conduits are mounted to the truck towable trailer so that the apparatus is self-contained.