pressure above the water in a tank is less than 1 atm ?
could yoube a little more specific?
Whatta is right. Compare to some bird watering devices.
The upper side of the tanks is airtight and maintained slightly under atmospheric pressure.
http://www.imagehosting.com/out.php/i429923_untitled.GIF, if pressure of air p1 plus pressure created by H meters of liquid is equal to pressure of air p2, water does not move. this is the way liquid manometers work. so, if there is no air in the tank, the water will not flood out of the cup that is less than ~1m from its ceiling.
So... is that place a resort for really lazy fishermen or what?
I think they are feeding the fish.
Same idea as a straw; I'm sure you've done this many times. Suck up some liquid or just put your straw into a liquid and then put your finger on top of it pull the straw out.
Why doesn't the water just fall out of the straw. This is due to the inside and outside pressures.
This would be a good photo to get the students attention when discussing pressure in a high school chemistry class.
I know a guy who tried to patent the whole inverted-fishtank idea.. but in practice I imagine it's a pain to keep the water oxygenated while continually removing any errant air from the top of the container.