Hi, new user here. I'm remodeling a basement bathroom including replacing the toilet in a 1939 era house. When I removed the old toilet (really old with all metal parts inside the ~5 gal tank), I found the old flange was virtually nonexistent. The only thing holding the upsidedown bolts that held the toilet in place was a thick, flaky layer of plumber's putty. So I need to connect a flange to the 5" inside diameter cast iron sewer pipe. I've never heard of a 5" inside diameter sewer pipe, but see the photo for yourself. The top of the pipe is flush with the concrete floor. There is what looks like another pipe inside the 5" one and that interior pipe ends about 5" from the end of the bigger pipe (and the floor). It seems I have a couple options. 1) I could chisel away the surrounding concrete and use a rubber transition to connect a PVC flange to the outside of the sewer pipe - if I can find one that fits a 5" pipe. That would be a lot of effort. 2) I could use PVC flange and insert it directly into the sewer pipe. By luck, it looks the the 4" inside diameter flange is about 4 7/8" in outside diameter, which may fit just right (or with a bit of sanding/filing) into the sewer pipe. See photo. If this works, it would avert the need to break through the concrete. My questions: - Does my description and options make sense? Am I missing anything important? - What is right way to address this situation? - If the right way is too onerous, would my option 2 work? Could I use PVC primer and glue to glue the PVC flange to the inside of a cast iron pipe? If not, is there a different adhesive I should use (how about silicon caulk)? My intent is to screw the flange crown into the concrete floor to add stability and take pressure off the glued joint. Thanks for your help.