Easier to screw it right to the backer board. Use galvanzized drywall screws that are long enough, but watch out for copper pipes. (screwing onto them) Your flange (if it's PVC requires the same primer and glue joint process as any other PVC joint. You may have what's called a slip flange. which means the "slip" is the same OD as the pipe size your using.

Hi, I must be going through the same process as you. Updating a bathroom.

I too, am in the process of laying backerboard and am unclear about the toilet flange. I got two differnt answers at Lowe's (flush with the tile, on top of the tile), two answers from Home Depot (both said flush with the tile).

Mr. Vila, what's the correct configuration?

Best Regards

It never ceases to amaze me how people would actually take the advice from a clerk in a store on how to do electrical or plumbing.

Considering many of these folks work just above minimum wages do you really expect them to know the right job?

For example I pay my top mechanics over $65.00 per HR in the envelope I am sure the old saying you get what you pay for normally is true.

Set the flange even with the tiles and even 1/8 -1/4" below as the toilet horn and wax gasket will take up the difference.

http://www.masterplumbers.com/plumbviews/2001/homecenter.asp