Sorry I didn't back to you on this thread the correct way to do it is use 99.9% isopropyl alcohol or denatured alcohol after blowing out as much of the DOT 3/4 fluid. I use a large syringe and flush line and caliper until they are free of all the old fluid. Drain and flush the master cylinder. Blow out everything to dry. Add the new and slowly bleed the line and make sure the new fluid is coming out clear from caliper.
I know some people seem to have issues with DOT 5. I did not understand why until one day I saw this one guy "help" bleed a brake system. He pumped up the master so quickly and forcefully pressing the brake pedal to the floor about 20 times and every time he wanted the other person to open the bleeder. He was making foam action in the master cylinder better than the food industry making whipped cream
, you have to be slow and very patient with DOT 5.
That why you can't use DOT 5 in ABS system because of its rapid pulsation piston it creates air bubbles in the ABS module.
I highly recommend rebuild the master cylinder and caliper if it at leases 15 years on DOT-3/4 any way, but I have seen it done with-out rebuild the brake system.
Oh P.S. All DOT 3, 4 & 5.1 are already synthetic blend don't pay any attention to marketing labeling with the word "synthetic" BS.
As for DOT 4 Plus it turns out its it was going be label as DOT 4.5 but end up become DOT 5.1 as a better more refined version for ABS systems.
I recommend you Read this about Bake Line Hose especially if they're more than 12/15 years old there already pass their life expectancy due to the way their construction and material used.
I also recommend replacing with an OEM part or if want with better longer lasting Braided Lines Hose made by Galfer, Venhill, HEL or EBC they should last way pass 30+ years due to the way their construction and material used.
Here is an explanation why
hydraulic driven brake switches fail at inconvenient times, it has nothing to do with DOT 5 fluid.