He posted the specs of the top part of the tank. It seems to be quite close to a 4'x2'x2' but the roof being sealed, both of the smaller sides of the tank cut open, and a 3'x1'x1' foot tank underneath joined in with a hole cut open on the side and sealed all the way around.
There is only 2 problems I can see with this. One, you'd need insanely thick glass due to water pressure - There's roughly 5 feet of pressure there, which is pressure most standard aquarium glass wouldn't be able to hold.
Secondly, my estimates are off, and a generalisation. I'm guessing my measurements would work with proper preparation.