The Dot 5.1 is just a better(higher boiling point)Dot 4 fluid. Stay away from Silicone fluids. Regular Dot 5 is suppose to have silicone and that is bad for our seals/master cylinder. All of the other synthetic fluids should be mixable. Just read the label and it will tell you.

I put speed bleeders in all the calipers, hooked up a small vacum hose, and just pumped the old fluid out(looked kind of milky and not super clean), when the reservoir got low, I just refilled it and started again, when the new super clean fluid started coming out, all the old was gone. I did the rear first and then the front. I used a bit less than one quart to completely flush the whole system out and to refill my reservoir.
This also took two people to do, even though I used speed bleeders.

Next time I flush the system, I will used a different color fluid to make sure the old stuff is gone. I plan on doing this every season not since I plan on doing a lot of autoX events.

BTW: I used Wagner Severe Duty Brake Fluid Dot 5.1 wholesale price was less than $6 per quart. retail was around $14


DeanoD
1997RS-NeverTurbo
http://ar.dsm.org