The only time we've ever used plumbing flux in electronics - at least in the broadcast industry - is to braze EIA flanges onto field-cut transmission lines.? This flux is fully removed before the line is used though.? First a dip and some swizzling in a dilute hydrochloric acid solution, then a dip in a dilute sodium bicarbonate solution, then a final wash in water.
This is always real fun with a 19 foot section of 9 inch hardline... :\
