Rusted closet flange

[Islander]

I have a rusted closet flange that was installed with 3” ABS pipe and the cement slab was cast around the flange. Now that the ring is rusted and removed I noticed the concrete under the metal flange was not level and to add to that the floor was tiled and the flange was below the finished floor. The amount of wax under there makes me think that two wax rings were used when the toilet was placed. I believe that I can make the repair by using a closet flange that will insert inside the 3” pipe and mound up some concrete under the flange to provide the right height and once the concrete sets, drill some holes and tapcon in the flange. Ive heard that that inside flange may not be code approved and also certain members of my family clog the toilets more often than what would one think is normal. My other thought is to drill whats left of the old ABS flange and separate the it from the pipe and glue in a new flange that fits over the pipe and proceed with the same cement idea as mentioned above. Any thoughts on how easy it is to unglue ABS fittings or what repair I should use? Thanks

 

[Terry]

The outlet of most toilets is about 2" which then drops into a 3" pipe.
I don't have a problem with the inside flanges in this situation. You're adding about 2" more distance of a smaller than 3" line on the vertical which is receiving from a much smaller trapway that is also directed downward.