Hi there partner! ive done this several times on my 11/12 '99 bikes...
The stock ENI .... holds a lot of energy/heat for sure.
I run water-wetter, and distilled water. (i'm in texas, no antifreeze needed)
here's my process:
1 - i lift the front end up (i use tie down straps anchored to ceiling)
2 - remove expansion tank cap on top, pull expansion tank hose off the very bottom (this drains exp tank).
3 - remove upper radiator cap.
4 - remove lower drain bolt, allow it to empty.
5 - lean bike over on the side the drain bolt is on, i do this by pushing the rear of bike in opposite direction since front is suspended from ceiling.
6 - squeeze each hose you can reach between lower and upper radiator, observe more dump out bottom.
7 - pour distilled water into top radiator and observe drainage at bottom, flush until it comes out clear at bottom, usually takes me about 1/2 gal of distilled water
8 - reinstall lower drain bolt
9 - reinstall lower drain hose for the expansion tank you removed in step 2, reinstall cap on exp tank. (dont put anything in exp tank yet)
10 - fill upper radiator with distilled water, squeeze hoses you can reach as you do so, fill upper radiator with as much distilled water as you can, then reinstall upper radiator cap.
11 - start bike, allow temp to go over 150F, that will open the wafer control valve and water will circulate in motor.
12 - shut off bike, slowly remove upper radiator cap, then remove lower drain bolt. observe more red fluid draining, squeeze all hoses you can reach, pour more distilled water into upper radiator, observe more red draining out of lower drain hole, do this until drainage is clear.
13 - repeat steps 8 and 10 and 11 and 12 until everything coming out of lower drain hole is clear.
14 - make your water wetter solution, and fill upper radiator, squeeze every hose you can reach, fill upper radiator completely.
15 - add your mix to expansion tank, fill the exp tank at least 1/2 way, but do not fill completely.
16 - put everything back together, ride your bike, get to full operating temps. Any overfill you did will dump into expansion tank, which will in turn dump onto the ground under your bike. If you underfilled the radiator during step 14, it will pull expansion tank fluid into radiator.
17 - after a ride or two (couple heat cycles), check expansion tank level and add as needed.
keep it classy buddy,
Jag