Rust appears in the toilet tank as a reddish brown tint. It is not rust in the common sense, but is an accumulative result of minerals in hard water. It grows over time, into unsightly streaks that seem almost indestructible. You can deal with rust in toilet tanks without using harsh chemicals. Common vinegar will break down mineral rust without all the toxic fumes that comes from chemicals. Vinegar is affordable enough to use anytime you see rust beginning to form in your toilet tank.
Remove the toilet tank lid.
Pour in 1 quart of vinegar. Wait 24 hours.
Scrub the tank with a stiff toilet brush. If the rust persists, pour in another quart of vinegar. Wait 24 hours and scrub it again.