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Disconnect the rubber line that goes up to the top of the brake booster. The one you want goes between the top of the PS reservoir and the booster and does a 180 turn before connecting there. Plug a 3/8ths inch INSIDE diameter clear tube (you can get a 10' piece at Home Depot for like $5) into the booster. Start the truck and pump the brakes to push the fluid out. You should also turn the wheels from stop to stop, so it will help to have the front off the ground. You can also use that tubing to flush your tranny whenever you get to it...
I used Mobil1 syn in mine which quieted mine down quite a bit and made it feel smoother turning as well. You can probably get away with two quarts, but I bought three and had an extra and a little more for when I did my tranny...
EDIT: You guys are quick -- I started the reply then got interrupted before I could finish it...