I have never been able to remove the square drain plug that you are supposed to drain the remaining oil from the cans from. I have tried to get it with the 7/16" box wrench suggested, but it just won't cut it. I can't find any other regular tools that can fit it there to get the job done. I did find some 8 point sockets from grainger, but hate to blow the money unless I have to. Any ideas?