drain water?

If water is from a municipal system with chlorination treatment system -it will sit fine for a couple of months if the caps are in place preventing bug entry.

I usually leave the tank full, to keep stuff from growing and in case of a disaster.
Just before the next trip, I drain and refill.

Here in this Az heat I drain it then put back a couple of gal to keep the valve from drying out. I do this once a month in summer. Bad things can grow in it. But I want the valve wet. I also keep water & toilet valve treatment in the bowl along with 4/5 5gal bucket of water in the trailer.

I'll leave freshwater in the tank if I know we are going back out within a few weeks, but if it is more than a month we will drain either at the end of the last trip or just prior to the next trip and refill with fresh water. I fill with chlorinated city water from home and have used water from the FW tank that has sat for several months with no ill tastes or odors.