Cathodic Protection system 1

Is this systems protecting the inside or outside of the tank/drum? Is the tank/drum going to spend a large portion of its time full or empty?

In order for cathodic protection systems to work, a electrolyte needs to be in contact with the material to be protected so the impressed current can be applied uniformly. This is a precondition that is unlikely to be possible for a tank bottom sitting on a concrete slab.

Cathodic protection can be used on the inside of storage tanks - if the liquid being stored is conductive. If this is a potable water application, see this from water world Cathodic Protection for Above Ground Storage Tanks

Waterworld does indicate cathodic protection of tank bottoms is possible, but the design must overcome e caveats above.