Water and your water tank

The RV water tanks are food grade. And as long as you don't have leaks, it's a closed system. Water doesn't go bad very quickly if ever though it might go stale so makes no difference if you fill the tank and leave it that way or not. Weeks or years later it'll still be fine.

What ever is the most convenient for you and your situation is what you should do. I'd leave it full just so it's not something else I'd need worry about if I were in a hurry.