First thing to do is use a turkey baster or other device to remove all the old fluid from the Master Cylinder. Then add fresh fluid. You can purchase a one way bleeder valve but the common 2 man method works just as well. The most common method is the tried-and-true two-person procedure. First remove the lid from the master cylinder (be sure to clean around the lid first, to prevent any dirt from falling into the reservoir). Make sure you start at the wheel farthest from the master cylinder, that would be RR, LR, RF, and end at the LF, and slip a piece of clear plastic hose over the bleeder valve, it should fit snugly. Place the other end of the hose into a clear container, such as a glass jar, submerged in brake fluid. Have an assistant pump the brake pedal a few times to build up pressure, then on a downward stroke, hold the pedal depressed slightly.
While he's holding the pedal down, use a wrench (Boxed End Only) to open the bleeder valve just enough to let a surge of brake fluid escape into the hose and container. Your assistant should then slowly depress the pedal to the floor and hold it there long enough for you to immediately close the bleeder valve again to prevent air from being drawn back into the lines. The key here is to keep the fluid level in the master cylinder above the minimum mark by repeatedly adding fresh fluid. Once you begin seeing fresh, clear fluid (with no air bubbles) coming out of the bleeder valve in place of the old, dark fluid, you can tighten the valve and move on to the next wheel.
Repeat this procedure on all four wheels, working your way toward the master cylinder, which should be your last bleeding point (unless another sequence is recommended in the vehicle's service manual). Just be careful when bleeding, to not let the master cylinder fluid level get too low & suck air into the system. This is very important on ABS systems, because if you let air get into the ABS motor, you may end up at the Dealer, or a brake specialist, to have them vacuum the brake system, or cycle the ABS motor, in order to remove the entrapped air.
