Check out this thread for instructions on using muriatic acid and alternate fluids for cleaning rust from gas tanks.
One of the alternates is simply vinegar which is a whole bunch safer than any type of really caustic acid.
Caution: Pay close attention to always add acid to water. Not the other way around!
An easy way to remember is do add ingredients alphabetically: A (acid) to W (water).
You run the risk of having the acid blow back in your face if you add water to acid since the water will react violently to strong acid. Adding acid to water results in a much milder initial acid/water solution
