Best way to flush the brake system?
 

Is it better to drain the system then put in the new fluid and bleed it. or just to start putting in the new fluid. I'm switching to Dot4 so how would i know when the old stuff was gone?

Drain it and refill it. Make sure your new fluid is a different color than the old. Bleed the system until only the new color comes out.

I disagree. If you drain the system you will have a lot more work to get all of the air out. The ABS will get air in it and will have to be bled as well as the master cylinder and all 4 wheels. You will go through twice as much fluid even if you get it right the first time. DOT4 is compatible with DOT3 or whatever you have in there now. If there is a small amount of the old left in it is no big deal. You are flushing simply to replace the old with the new, primarily to increase the boiling point and remove moisture. It's not like it has HINI influenza virus in it. Don't overthink it. Colored fluid like ATE blue helps but you don't need to obsess about completely replacing all of the fluid. If you flush 1/2 to 1 quart of new fluid through the system you will have replaced most of the old fluid and you need not worry about the remnants.

If you think about it, it's not much more work than bleeding it, then filling it, little by little until you've flushed the old out with the new. It's not like we have this massive reservoir that you can dump an extra quart or two in at a time to flush it.

to each their own. Nothing wrong with either approach in my opinion.

The process of bleeding isn't the question. Getting air out would be the same for either method. I'm more asking about what is best to change the fluid completely. And I think at this point I'm just going to go with the blue fluid so i can see the change over.

Sorry, misunderstood your post then. Yeah go with the ATE Blue.