Great! Wondered what that was for. Sadly, mine that I got at Tractor Supply off the shelf was missing that important cap. I tried a Pepsi cap (too big) and water bottle cap (too small) but none will work. Anyone have any ideas of what kind of cap will be a good substitute?
how do you top fill it? That water comes out the bottom as fast as you put it in the top. So by the time you can get the cap on half the water is gone. This didn't come with instructions.