I guess we may be on the extreme opposite of most.
We never drained our fresh water tank before short term or long term storage.
We keep our tank full and ready for use at all times, and we travel with a full fresh water supply.
We always use water from our home supply when possible.
I will sometimes introduce no more than 2oz of chlorine directly into the water supply hose if we run out of our home water supply, and start using the campground water supply, half filling the tank before departing for home, or filling completely if we know we will be using that water up in a few days.
I do a lot of washing during our trips, and this ensures we always have a fresh water turnover that won't have the time to grow anything in our tank.
Dan & Loretta, US Army Retired Aero Scout Pilot
2012 Fleetwood Providence 42P Class A/DP
Spartan Chassis, 8.9L Cummins 450HP