Pooch,
Boiling, after allowing it to rust an appropriate amount of time(depending on amount of rusting)stops the rusting and at the same time turns it black.

gunsaholic,
You can use either stainless or carbon steel for the tank.It should be boiled long enough to heat the metal to the point that it will dry quickly when removed and tilted so all water runs out.Pouring boiling water on it will work, after a fashion, but is not nearly as satisfactory as boiling in a tank.
Mike