A bad corrosion graphic?

In recently searching for sacrificial images online, I came upon the following graphic (at opentextbc.ca)...

...and I think it has a pretty significant error in representing the science of how sacrificial protection from corrosion works.

I'll put my reasoning after the jump...




My understanding - and I am 100% open to being corrected here - is that the sacrificial anode (shown as a vaguely bell-shaped thing on the right in the above graphic) corrodes and gives off electrons (Mg --> Mg⁺² + 2e^-, for example...LEO...OIL). The electrons then travel (via wire if the sacrificial is not in direct contact with the object being protected) to the object being protected. As long as the electrons keep flowing, the protected object can't corrode.

Admittedly, somewhere in the circuit, ions have to travel - positive toward the protected object, negative toward the sacrificial - to keep the charges balanced. In AP chemistry we talk about this as a salt bridge, allowing the ions to drift as necessary to complete the circuit and maintain charge balance.

In the above image, though, there are arrows (labeled "no power source is needed") leaving the protected object (a buried tank, maybe a septic tank) and going to the sacrificial. Then there are arrows labeled "protective current" going from the sacrificial to the buried tank via the dirt.

I have no idea what would be leaving the buried tank via wire unless Benjamin Franklin made the diagram. And the 'current' - assuming they mean electrical current / electrons - doesn't travel through the soil from the sacrificial to the buried tank.