Went to replace a toilet and turns out part of the cast iron flange has corroded. This is the old lead/oakum setup. I've cleaned out all the gunk, and tried to bust out the old flange by taking a chisel and hammer to the lead. After about an hour it's still sitting in there pretty good.
I am planning on putting on a new PVC flange with a rubber gasket. It's designed to sit inside the old cast iron pipe and seal with a gasket. The old flange is flush or a little below the tile.
Question: Is it necessary to remove the old flange? The new one will fit right on top of the old one, with the lip sitting nicely on top of the tile.
Other question: If I go this route, is it necessary to bolt the new flange to the concrete slab? It doesn't move around when it's sitting on the old one.