The house used to be on a septic, hydrogen sulphide gas is what ate away the top of the cast iron, the copper will go next, it only affects horizontal piping, all the vertical stacks will still be fine. If you want to do the church a favor tell them it is in their best interest to cut out all of the existing three inch horizontal copper waste as well, it doesn't last that much longer than the iron does once it is exposed to hydrogen sulphide.The house is on city sewer. I will take a close up shot tommorrow of the copper/cast connection and post it.
That one looks leaded in, but they make tap san tees with threads on them for copper stub outs on sinks. We do all our hospital work in cast and copper drains.What makes the seal? I see tons of cast, but almost never see copper DWV. Especially a connection between the 2.