Retired plbg1
If you have 4″ pipe then you can cut it flush with the floor and get a flush 3″ flange and fit right inside of the pipe. If it is 3″ insde a 4″ pipe then you have to take a saw and saw inside and just cut the 3″ flange about a 1″ wide up to pipe on two sides and take a hammer and screw driver and cut the piece out and then go around the flange with screw driver and take it out. Also cut flange flush with floor before you saw out pieces.
