Here's my trick that I used on a square plug: Take a ratchet extension, 6" or 12" long, 3/8" or 1/2" drive, whatever fits over that plug "UPSIDE DOWN" and put a big wrench on the exposed end. But as suggested earlier, spray with wd40 then tap a couple of times with a hammer first.
IF you HAVE TO DRILL, Autozone sell some reverse direction drill bits. as you are drilling, the bit heats up the fitting and walks it out backwards. Works everytime. DO NOT USE AN EASY-OUT, IT WILL BREAK OFF IN THE HOLE!