I am replacing my toilet and found that the cast iron toilet flange is broken where one of the bolts that hold the toilet should go. This was a crescent shaped slot, but the outer rim is broken and missing. I was going to replace the flange, but can't see how it is fastened to the drain pipe. The house is on a concrete slab, but I can see the drain pipe move slightly when I pry on the flange. How do I remove the old flange, or is there a way to repair the existing flange?

Thanks,

Wornout

Your toilet flange's secured by a poured and caulked lead and oakum joint.
Since they make a repair kit, (see image) for broken flange slots a replacement flange isn't needed. Simply slip the repair slot and closet bolt under the broken part and reset the toilet. Good luck, Tom

The repair kit mentioned is the most common repair done. It you want to replace the flange, put a rag or something in the pipe so nothing falls into it and gently break the old flange off by hitting it from the inside. Then install a compression flange inside the cast iron pipe. A compression flange has 3 allen screws on the top and a rubber ring that seals the pipe. Remember to secure the flange to the floor with plastic anchors and screws or tapcons.