Hi, I'm trying to replace a broken piece of what I belive is cast iron pipe with new pvc on a bathrrom sink. Not positive its cast iron, but the piece that broke was about a 5 inch long connector piece threaded on both ends. One end to the main pipe and one end going into the plastic under the sink. The threads from the connector piece came apart and it was very corroded. So now I need to install new pvc but I'm not sure how to attach it to the metal pipe. Any thoughts?
You describe what is most likely a piece of galvanized pipe that was screwed into a T on the drain pipe. You just need a male threaded PVC adapter (with 2-3 flat wraps of teflon tape wrapped clockwise only on the threads as the threaded end faces you) to screw into the T. Clean up the threads on the T first.