Built an IC this weekend and am not sure how to be sure it is clean enough.
I wiped it down with dish soap and boiled it, but still had some tarnish and dark spots on the copper. I attacked it with Barkeerpers Friend and a toothbrush and got it looking very clean and shiny. Probably spent more time cleaning it than I did building it. The toothbrush bristles are black now.
But once it dried, some dark spots reappeared. Not as many, but they are still there.
Easy way to clean is boil with water and white vinegar. Don't remember the ratio, but a search should turn it up. BKF and toothbrush would be fine if you were in prison and had nothing to do all day. Reminds me of escape from Alcatraz.
If you scrub the tarnish harshly you are removing it to clean metal that will then tarnish. That would be a never ending cycle until there is no metal left.
I would do the boil a couple of times before first use, then put it in the wort before flame out and the heat will sterilize it.