Originally Posted by
Waterlogged
Copper is like aluminum in the manner that it forms a protective layer when exposed to air. If exposed long enough (think decades, but it can happen much soon if conditions are right), it turns to a green patina which is actually part of the corrosion process. By hitting the copper with vinegar (acid), your exposing fresh copper to the air again and depending on how long you let it sit exposed to the vinegar then air, there is a slight chance you may get a patina in the rad which means you'll have to start all over again. I had it happen with my BIP back when I was but a true n00b.