leaving fresh water in tank?

We're on city water and I fill mine every time we get back. We go camping every two weeks so it sits that long before I drain it again. (we travel with about 1/3 tank).
I prefer to fill it because when you drain it there's still a quart or two of water in the tank and it's a lot easier for that little amount of water to get nasty then there is a whole tank of city water with the chlorine they add to it.
It's also nice to have and extra 40 gallons of drinking water around should an earthquake hit us.

I would think it would be best to leave it full with a little bleach in it.
Air is your enemy.

I drain every time,

I drain mine everytime