It's right under your driverdoor inside the frame rail. There is a yellow 1/4 turn valve that will drain the water. I suggest a 20oz plastic soda bottle cut in half. That way you can see just how much water was in the fuel and any other debris.
2008 F-250 Lariat 4x4, 6.4L, 4 tires, brakes, windshield, windshield wipers, tailgate, bumpers, blinkers, headlights, spare tire, rear bumper, hood, antenna, driver AND passenger seats, speedometer, radio, steering wheel, & spare set of keys!