A mobile chemical mixing and injection unit adapted for use during the extraction of an oil/water/sand slurry from an oil field storage tank wherein said tank has a body of accumulated sand therein. The unit comprises a motorized truck body having a flat bed with a water storage tank and two mixing tanks mounted thereto. A high pressure injection pump pumps water from the water storage tank to the oil field storage tank and creates a slurry. The slurry is pumped to an adjacent settlement tank hopper where the oil, water and sand will stratify. An effective amount of a flocculating agent, coagulating and surfactant are mixed in each of the water filled mixing tanks and then pumped into the slurry to facilitate separation of oil, sand and water. The high pressure injection water and the water for the mixing tanks are replenished by pumping water from the settlement tank hopper thereby ensuring a continuous process until the field storage tank is cleaned.