FASS Fuel Systems Diesel Fuel Sump Kit (SK5501). This Fass SK5501 is a universal Sump Kit and fits MFG PN: SK5501. Installing a FASS Fuel System has NEVER been easier! FASS stands for Fuel Air Separation System and is a combination diesel fuel lift pump and fuel filtration system that is designed to improve your diesel trucks fuel mileage, engine performance and extend the life of your diesel injection system.