I should preface this with the fact that there is NO underground copper in my old county. Not sure why, but there isn't, so we never worked with the stuff. That said, Domestic lines were 200 PSI Poly, and everything else was PVC. We always tapped using all brass parts. Anything that wasn't PVC was brass, at least underground. We would use Galvi on pump setups but thats it. When you work with metal underground, do you use brass, galvi or copper? If your using Galvi, why???? I've dug up too many balls of rust that turned out to be a fitting.