Copper is on the feed side in house plumbing, not USUALLY in the drains. Although I have seen it there.

With my design idea, the copper is no where near the generators. As a test, I have a piece of copper at home, sitting in a jar of very strongly mixed KOH and water. Looks like no damage so far, has been sitting there 3 days. I will give it a week and carefully inspect the copper. Will post back results.