I have a bathtub spout that has a "half-dollar size metal plug on the bottom side of the spout. This "plug" has a long slit in the center. I am assuming I have a slip-on spout, but cannot be for sure. Problem is, I can't take out that plug to reveal a hex screw. I've tried with the largest screwdriver I have and this plug must be corroded on. Is there a special tool to remove this plug?