Mercury - Inline Fuel Filter Under-Cowl Fuel System Clear Polymer Housing 877565T1. Overview. There's something reassuring about knowing the fuel running into your outboard is clean, steady, and free of anything that could slow you down. The Quicksilver 877565T1 Inline Fuel Filter gives you that quiet confidence. It sits under the cowl doing simple, honest work - catching debris before it ever reaches your engine. When you're idling toward the flats at sunrise or cruising back across open water