Removed old toilet and existing flange was rusted through. It was a red flange with pvc fitting onto pvc evacuation tube. I purchased a new flange that is identical to the existing one, then chipped away the rusted flange leaving the pvc part of it still attached to the pvc evacuation tube. How do I break the seal between the two pvc pipes so I can remove the old one and drop the new flange on? I have tried liquid wrench on the joint and a lot of muscle, but that isn't working. The pipe is even with the floor and there isn't room to cut it away. Any ideas?

Those PVC pipes aren't coming apart. The glue is often stronger than the pipe. You can buy a flange repair kit made for this situation.

Is the pipe 3" or 4"? Is the flange glued on the inside of the pipe or the outside?