There the oil sand is fed into tumblers where steam, hot water and caustic soda are added to form a slurry and condition it for oil separation. The slurry is discharged onto vibrating screens where large material is combed out. Then the slurry is fed into four Primary Separation Vessels, deep cone vessels designed to recover most of the oil. Froth floats to the top, sand settles to the bottom and the middlings, the clay and small particles, are pumped to Tailings Oil Recovery. Two Auxiliary Settling Areas, smaller versions of the primary units stand by to assist. The oil primary froth floats to the top, the sand settles to the bottom, and middlings are pumped to Tailings Oil Recovery vessels where the oil froth from the tailing oil recovery vessels is recycled again to the primary separation vessels to improve its quality. There is a whole lot of recycling going on to get all or very close to all the oil extracted.