We are tiling the floor. The orig.floor is wood so we have to put down backerboard. The flange of toilet is a metal one under a lip of PVC that is glued to the 4" PVC closet pipe. We cut a hole in the backerboard where the flange currently is. We used a Two Finger Toilet Flange that attaches to the existing flange and has a PVC sleeve that slides into the 4" PVC. After allowing for the motar and tile we still need 1/2" to get us up to the new floor height. Can we use a second flange extenter on top of the other one or is that a bad idea. Is our only recourse to craw under house, cut off existing 4" PVC coming up through floor, put new PVC up through floor and have flange rest on the backerboard? We want to tile up to the flange but not have the flange rest on the tile. Do not want to drill holes in the tile. What the best course of action?