empty completely fill up with 1 part bleach and 10 parts water let it sit for a
day
empty and rinse a few times. If scale marks are still visible run vinegar over
the marks
and let it sit for another day. Rub off (should have dissolved). Rinse tank
several
times until the smell of bleach and vingear have gone. Fill and put a double or
triple
dose of dechlorinator (that treats chloramine and heavy metals) and leave for a
day or
so and rinse and rinse. Basically be paranoid in getting rid of the bleach.

Thats what I would do anyway.