Nope, not kitty litter, but close. Small bits of sand and other solid contaminants that fell out of the fuel flow and settled in the bottom of the bowl. Remember the fuel you're putting in your truck is coming out of an underground storage tank that's been around a few years. There'll always be stuff in it - it's never gonna be pure. Good primary filters not only filter the fuel, they also give crud a chance to settle out, which helps your secondary filter do an even finer job of getting stuff out and helps it last longer.