Advise on the proper fitting to convert my 3 inch copper waiste to 3 inch pvc

Hey Wesley...

You will want to purchase a MISSION or PROFLEX-style banded transition clamp.. see picture below.

These are sometimes available at the home supply stores... otherwise, off to a PLUMBING SUPPLY HOUSE to order a:

3" pvc x 3" copper mission clamp. This is a legal and reliable way to make this transition.

Let us know if you have more questions...

MARK