I have a 3" copper waste line in my basement (exposed). I had a plubmer come in to look over some other work I needed done. He told me the line was rotting/corroding from the inside out and that it only lasts 30 to 40 years. I can see no marking on the copper pipe but the brass/bronze fittings are stamped DWV. There are some green spots on top and bottom like it had gotten wet at one time. Line is approx. 50 years old. How long should this last? Thanks in advance.