The most convenient way found to change/monitor the anode rod was to join the threaded plug for the drain hole and the sacrificial anode in to a combo item. That's why the rod happens to be in close proximity to the threaded drain hole plug. The anode could have been located anywhere in the tank and still have worked well.
There is an electrical aspect to sacrificial anode that has nothing to do with threaded plugs. Because the anode is a different metal than the tank,there is a weak electric current in the water which is part of the process.
