You are right about the copper and iron. I only ever saw one copper line split. Probably soft copper. My iron lines were installed over 30 years ago if you look at the picture you can see rust on the wall from the drain valve. But you should see the rust under the compressor tank from the auto drain valve. Pex would be a good choice and easy to run. When I did mine Iron was the way to go. Now they have special air compressor plastic lines, Northern industries sells rapid air in kits 3/4 inch that would be something to look at. Easy to install from what I was told.
