Abstract: A containment and circulating system for drilling fluid is provided having generally circular tank means for receiving drilling fluid from a well during well drilling operations and from which the drilling fluid is withdrawn and injected into the well. The system incorporates a plurality of generally cylindrical tanks having cylindrical side wall means in normal relation with a substantially planar bottom wall. On opposed sides of each circular tank is provided angulated flow directing walls which intersect both the side wall and bottom wall. The flow directing walls receive the radiating flow from the impeller and direct it upwardly along opposed portions of the cylindrical side wall of the tank. An impeller is centrally located at the lower portion of each tank thereby inducing radiating flow of drilling fluid toward the lower outer wall structure of each tank.