You need the bow in the middle of the tank for the water pick-up line that goes to the pump, this way you always will have water at the pick-up line if you are not level. In the winter I have put a little RV antifreeze in the fresh water tank, then in the spring fill the tank a little and drain and repeat a couple of times. The RV antifreeze will not hurt you as it is food grade. After you have cleaned the tank of antifreeze then run the pump to clear the lines with the fresh water in the tank.
I also use bleach in the tank when I clean it the first time and pull that through the lines then rinse the lines once more to remove the bleach. Our water is clorinated, so if it sits in the tank for a while I do not worry about adding a little bleach later. Goose