Break line flush on a 1996 Mercury Mystique.

Are you trying to do this for general maintenance or to solve a problem?

The safest way is to open the bleeder screw to let the old fluid dribble out and to loosen the reservoir cap slightly so a vacuum won't build up and inhibit the free flow of the fluid. Let the fluid drip from one wheel first. When the reservoir is almost empty add new fluid from a sealed container. Keep bleeding that first wheel until clear fluid starts coming out, then move on to the second wheel. Don't let the reservoir run empty or air will enter the system, and don't keep any containers of fluid open any longer than necessary because brake fluid loves to suck humidity out of the air. That can lead to brake fade and corrosion.

There are tools to make this job go faster. One is an air-powered vacuum pump that pulls the fluid from the bleeder screws. There is also a pressurized "bleeder ball" that is attached to the reservoir but not many people use them anymore.

You can speed up the process a little by stroking the brake pedal, but never press it more than half way down to the floor. There's two reasons for this. First of all, crud and corrosion build up in the lower halves of the two bores in the master cylinder where the pistons don't normally travel. Pressing the pedal all the way runs the lip seals over that stuff and can rip them. Then you'll need a new master cylinder. Second, there will be a difference in pressure in the two hydraulic systems either from that ripped seal or just because one bleeder screw is open. That pressure difference will cause the pressure-differential valve to move and turn on a switch which turns on the warning light on the dash. That switch is spring-loaded to self reset on every car in the world, ... Except Fords. Getting it reset can be extremely frustrating.

When you're done fill the reservoir as full as it was when you started. Don't fill it to the top unless you recently had the front brakes replaced. When the front ones are replaced the pistons have to be pressed back into the calipers to make room for the new thicker pads. The fluid behind the pistons is pushed back up into the reservoir. If you filled it previously, that fluid will spill out and make a mess. That's why the oil change guys never top off brake fluid as part of the service.

Caradiodoc