I have 40 years of experience as a Water Quality Research leader at a major University.
1) The safe recommendation is a chlorine treatment followed by a good system flush to eliminate bacteria such as e-coli,
2) I would worry more about bacteria contamination during warm months especially if you are filling tanks with water from non treated sources (well water or springs)
3) Draining and flushing with chlorine treated city water should be sufficient prior to trips when your unit has not been sitting for long periods of time.
4) If you ever have an algae contamination be very concerned about contamination. There should never be any algae unless you are using contaminated sources of water.
We use our unit every month except January so my main line of defense is flushing with city water except during the summer when I like to chlorinate the tank once or twice to be safe. Reality is if you do not contaminate your system and use treated water there should never be an issue with e-coli.
Be safe do not be sorry.
Finally, I have conducted research studies in rivers subject to agricultural and wildlife contaminated runoff, finding high levels of e-coli contamination and where we find it (e-coli) is unpredictable.
