A method and a settling tank for use in separating a solids containing fluid, such as a drilling fluid. The settling tank includes a settling compartment comprised of an inlet and an upper outlet so that the fluid passes through the settling compartment generally in a first direction from the inlet toward the upper outlet. Further, a backwash fluid source directs a backwash fluid within the settling compartment generally in a second direction which is substantially opposite to the first direction. The method includes the steps of passing the fluid through the settling compartment generally in the first direction and directing the backwash fluid within the settling compartment generally in the second direction. Finally, a method is also provided for clarfying a solids containing fluid using a settling tank, wherein the settling tank is comprised of at least three isolatable settling compartments connected in series.