Originally Posted by Ed_The_Gypsy
In order for a sacrificial anode to work properly, it must be in electrical contact with the protected material. Otherwise, both materials corrode away. Electrons must be able to flow from one to the other.
Good point-- there's still at least a couple threads in contact with the tank. Plenty of surface area for electrons, not so much static friction (or corrosive welding) that we can't break the threads free of each other. Teflon tape is what, about a quarter-inch wide and the threads extend for at least a half-inch?
There used to be a big deal a few years ago with insulated (dielectric) water connectors. The idea was to minimize the transfer of both electrons and thermal energy. I wonder how that's doing.
Submarines have hundreds of zinc anodes at various locations. They're about the size of a brick and bolted onto the hull or inside a tank. Lots of fun to track down during maintenance & drydockings, or if one somehow works its way loose and starts rattling around.