I am remodeling a 50 year old home and I have taken out the wall hung sink, but the drain pipe extending from the wall is still there. I have no idea how to get this out. It appears to be inserted in a cast iron pipe, but I don't think these are threaded. How do you remove this and install a new one? I have removed the drywall from behind it to get a better look at it and still don't see any way to get it out. The one I bought has no threads on the end of it. I'm a novice, so please excuse my ignorance. Thanks!