I can't really see the point of letting it fill and empty all the time? Whilst mine doesn't dry out, it is on a permanent mooring up the river Tamar, tethered to a bouy and at the start of each season I fill the ballast, close the valve and vent and change the water about every 6 weeks when I remember. I did put a bit of chlorine in the tank one year to kill any moluscs who were swimming around looking for a place to attach themselves to inside my tank, but I don't know if it was needed?