Fresh water tank, contaminated?

Run hot and cold at all faucets. Sink, basin, shower, toilet, and outside shower if you have one. You want the chlorinated water to fill EVERY line. Then let it sit for two to four hours before you start flushing it out. If some line, like the outside shower cold water line, for instance, is left full of contaminated water any bacteria that survive can then work back into the rest of the system.

That is not likely (from a Sanitary Engineering Perspective) but why risk it. It COULD happen.