I'd get a soup plate and then slide the glass very carefully over to the edge of the table, and let the water run into the soup plate - it doesn't have to run onto the floor.
They studied it a little bit, but they couldn't spend all day finding out what to do, so they finally picked up the other one, and the water went out again, all over the floor.
On the way out I said to my waitress, "Be careful, Sue. There's something funny about the glasses you gave me - they're filled in on the top, and there's a hole on the bottom!"