If there is a lot of air in the lines, getting it all out can be kind'a tough. Pressure bleeding is the best way to get ALL of the air, plus all of the old fluid out of the system. Brake fluid will, over time, absorb water out of the air . . . which leads to all kinds of problems eventually. You can go out and buy a high dollar commercial pressure bleeding system, but if you are just doing one car every year or two, you can make a cheap one that will do the job.
You need an extra brake fluid reservior cap. cut out a piece of rubber the size of the inside of the cap and glue it with a little silicone (this is to help the cap seal to the top of the reservior. Drill a hole in the center of the lid big enough to push a tire valve stem in. I've gotten away with just pushing it in tight and not sealing it, but I guess you could use a little silicone here if you want to.
Once you have the cap, fill the resevior, put the modified cap on it and attach a small bicycle pump to it. Now keep a very slight amount of air pressure pumped into the reservior (too much pressure can bust the reservior open) and keep a eye on the fluid level and have someone else run around under the car opening the bleeders, one at a time. When they open the first bleeder (you can go in any order, but I start with one of the back ones) have them leave it open until the reservior is 99% empty (a pice of vacuum hose pushed over the end of the bleeder an ran into a container will catch the old fluid and keep the EPA and tree huggers happy . . . and keep the stains off your garage floor or driveway . . . etc.)
Refill the reservior and go at it again. Don't stop a the first bleeder until the fluid coming out looks as clean as the new fluid your pouring in. You may have to refill the reservior a time or two. Once you've got the first one running clean fluid, move to another one. When it is running clean fluid, move to a third one; when it's clean, move to the last one. When it's clean, top off the reservior and put your regular cap back on. Now your brake system should be full of fresh, clean, air-free fluid.
