So I've read that the biggest risk with buying a used tank is whether or not Cu has been used in the tank. I read that Cu can not be washed out of a system. My question is: If I were to buy a used tank, not knowing whether or not Cu was ever in it, but all new equipment, would this risk still be a problem? It seems unlikely to me that Cu would stay on the glass. Is there a method to washing a tank, thoroughly, without using harmful chemicals?