A method for removing processing oil from thin sheets of microporous plastic material is comprised of a tank having a liquid zone in its bottom portion which is divided into three sub-tanks having decreasing depths extending across the tank. Heating coils in each sub-tank vaporize the solvent to form a cleaning zone, containing vaporized solvent, above the liquid portion, and condensing coils located at the top of the tank condense the vaporized solvent and deposit it into the deepest sub-tank which also is supplied fresh make up solvent when required. A series of rollers feeds the material through the tank, from the side having the shallowest sub-tank toward the side having the deepest sub-tank, while repeatedly passing it between the cleaning zone where solvent is condensed on it to clean it, and the condensing zone where it is cooled to a temperature below the temperature of the vaporous solvent. Precondensing coils located medially in the tank between each pass of the material as it extends between the condensing zone and the cleaning zone and vice versa, define the extent of the cleaning zone and direct condensed solvent onto the material to wash said material.