I'm no engineer, so I guess I should have stayed at a Holiday Inn...
My 3 year old has a habit of pulling the stopper out of the tub drain. It's an old tub and for some reason I have a hard time getting it back in. I always get it eventually, but I'm guessing there's a trick to it. I attached a picture so you can see what type it is.
If you don't stand behind our troops, please feel free to stand in front of them.