I'm getting ready to install a toilet flange in my unfinished bathroom (in the basement so the flooring is a concrete slab and will eventually be ceramic tile). There is currently a 4" stub out sticking up out of the slab for the toilet drain. I thought I could simply cut the pipe down closer to the slab and glue a flange to the inside of the pipe but a friend recently told me I would have to chip the concrete around the drain pipe away in order to install the flange (meaning the flange would be secured to the outside of the pipe). Is that correct? My next door neighbor just installed a toilet (with the same set up I have) and he didn't chip away the concrete floor around the drain pipe for the flange installation. Thanks in advance!