How can I attach a modern pvc waste pipe intersecting into an old existing 1 1/2 inch copper waste pipe?
There are specialized fittings for this use. The two most common are the banded or mission coupling, a flexible rubber coupling with a stainless steel shield and two band clamps, and the Fernco brand flexible couplings. The mission coupling will have a thicker wall on the end to receive the copper pipe to make up for the smaller actual diameter. The Fernco brand does not have a stainless sleeve, but does incorporate the two band clamps. Your local plumbing supply store will be able to order these for you if they do not have them in stock.