...Yet, to make it doubly safe - we do drive ground rods down about 35 feet (12 meteres) and use 2/0 copper conductors within 30 (10 meters)feet away from the tank to prevent lightning strike damage to the tank...
This makes no sense and is a complete waste of time, material, and energy. The only way to POSSIBLY prevent damage from lightning is to install a conventional LPS in compliance with the NFPA 780. In all honesty, the installation you describe above serves no purpose.
We do not hook the grounds (earths) up to the house grounds for obvious reasons, if we can avoid it (mostly at all costs), for obvious reasons of not letting the lightning strike into the house.
Anytime you connect an object to earth at one point and then connect another object at another point, a potential will be established as ground potential rise occurs at or near the strike termination point. This difference of potential is what allows hazardous currents to flow and/or allows inductive arcing between nearby objects at these differences in potential.
BONDING of anything and everything conductive together and to the service grounding electrode system is usually your best bet.
Fancy and excessive GROUNDING techniques have never been a solution for electrical nor lightning issues. (except in extraordinary circumstances)
