I don't think he's messing with us.
Since the left and right sides are identical let's just concentrate on the left side. I think D is the part that goes over the tank. Sections A, B, C, D, E, F, and G are all filled with water during normal usage. As the water rises above A it will also rise in G and pour out of O into the sump. The pink check valve is to start the siphon and remove any air that might get in there. In the event of a power failure the level of water in parts A and G will be equal and the siphon will be maintained throughout the entire red section. When the power starts up the siphon will continue.
Of course I don't even own an aquarium so I could very easily be completely wrong.