I actually flushed it the first time by draining the fluid into a 5 gal bucket and dumping the bucket into the old coolant barrel at the auto hobby shop on base. Took a bit more work but made me feel environmentally friendly..lol.
Woody, did you shoot the compressed air into the overflow tank? I'm currently running about 30% zerex coolant, 70% distiller water for the TX summer but am worried about corrosion.