I just finished my coil last week, and did a lot of soldering on my coil. I had excess flux in it and really didn't know what would be the 'proper' thing to do, so.......
I put the thing in my kettle boiled it for about a half hour.
Then flushed it with ground water to get most of the softened flux out.
Then I hooked up the pump and ran the boiling water through the coil.
Then I added oxyclean to the boiling water and ran that through it, too.
Then one more flush with straight boling water, and called it done.
I caught the output of the coil in a bucket and saw that I got a ton of greasy flux out while doing this whole thing.
I used the coil the next night while brewing, but not in full HERMS mode. I just used it as a chiller, but I ran the wort through the coil and had the coil in ice water. The beer I made that night seems fine (no oily surface, nice big fluffy krausen, etc).
Just my $0.02.
Ground Fault Brewing Co.