Tropical Fish Care Tanks: Here is a step-by-step guide to a Iwagumi style set up I recently did. This is a 5 gallon Fluval tank, so really small, and sits on a bookcase in the living room. I will post more pics as it grows in!
"The air in the vertical tank was pumped out and displaced by water. So the water is pushing down on the horizontal tank. There is no active pump required to mantain the vaccum. Once its stablished it stays that way.