Just did a complete brake job on new to me 07 Denali with 75k. I partially drained and filled the master cylinder via turkey baster 2x's a couple months before doing the brake job. I replaced everything in the brake system including new stainless hoses, drained the calipers and was still surprised at the rust, metal, and one rear caliper had nasty grey fluid almost resembling bad gear oil. I am lucky enough to not live in a rust prone area where lines rust out etc. I do this on all my vehicles every 2 years or so and always get a nice performance difference in braking. A fluid flush will cost anywhere from $7-$16 bucks depending on what fluid you buy. Our rides usually spec Dot 3 but you can use 4 or 5.1 safely, I used Castrol Dot 4. For a homemade bleeder setup I used a plastic fitting from a harbor freight bleeder kit and some clear hose fed into a RC car fuel bottle with a little fluid added to prevent air getting sucked back in. I would have preferred a larger hose over the bleeder nipple but didn't have one available. Cheap, easy, usually nice performance bump and keeps you and the family safe.