How often should I sanitize my fresh water tank during camping season? I sanitized the tank when I de-winterized the system (I of course did not sanitize the alde heater, that's a no-no I believe). How long can the water sit in the fresh water tank unused before I should be concerned about sanitizing the tank? I might go about a week at a time without using water from the fresh water tank. We will be using a Brita water filter container to drink our water. Thoughts?