There are actually two holes there. But one must be pluged. Both should be pluged. I can't imagine why one of the holes isn't pluged. Go to any Hipo shop with the size of the plug or check your local plumbing place Lowes, HD. if you can reach it take the other plug with you to compare the size. You will need a allen wrench to remove it. I believe they are the same size. Just put the plug in the orignal empty hole to match.