If there is no water present in the tank you should not get any new growth. Then the only way to get bacteria is from an infected supply tank. It happens occasionally.

If I had bacteria and used a good biocide on it I would consider it done unless I got reinfected.

I have driven some of my diesels a decade or more without infection.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.