BOSS Separator PRE-FILTER OPTIONS Default. Three different options are available for a pre-filter system to prevent larger particulate from entering the system. The BOSS oil/water separation system is supplied standard with a pre-filter in the form of a Y-Strainer. This prevents any large material from entering the separation system. Other options are available as follows. 1- Basket Strainer. 2- Bag Filter. 3- Hydro Cyclone (Solids Removal)