I just read the thread about the rotten sub floor and I have a similar issue. I have a pier and beam house. The waste pipe comes up through a hole in the floor and (before removing the toilet) the toilet made contact with the flange and was sealed with a wax seal. The only unique issue here is that the hole that was cut around the 4" waste pipe is 10" in diameter. I am guessing that toilet weight was able to be held by the surrounding floor, but all the pictures I have seen about replacing a toilet usually has the flange flush with the tile floor. In this case, there is a several inch gap all the way around the waste pipe and while the pipe is fairly solid, I am concerned about its ability to get a good seal and also carry some of the weight of the toilet. Also, the flange is sunk down about a 1/2" below the floor level. What would anyone recommend? The waste pipe looks like it is good. I am wondering if I should go under the house, patch up the hole to fit the 4" pipe and then back fill with portland cement. Any thoughts?

I would certainly get under the closet bend and brace it up so the flange is level with the floor.with a 2 X 4 cradle. (Looks like a U ) you may then patch the floor if you wish. Goodluck Tom