Back in pre-ethanol days I used to store full to minimize the chances of condensation in my tank. But now I store nearly empty, but treated with stabil or seafoam and then in the spring, squeeze the bulb and drain out a gallon or so from the bottom of the tank and then fill it to the top before starting it in the spring. The storage season here in Maine is longer than in most places so that means if I stored full, by the time I got around to burning that gas, it could be 8 or 9 months old and according to my mechanic, they've had a lot of trouble with ethanol/fuel that old. I accept that due to my tank being nearly empty all winter, there will be some water accumulation in my tank, but I have both an inline screw on type, and engine mounted screw on type filter that should remove the water, and in the spring I remove the fitting that plugs into my kicker motor and squeeze the bulb to drain out about a gallon from the bottom of the tank before pumping in over 50 gallons of fresh gas. I guess that what you do depends on which you think is the greater evil, some water in the bottom of your tank, or possible phase separation of a whole tankful of gas that you'll be burning in your motor. I can see both sides, but think the water is easier to detect/remove so drain my tank and then start fresh next spring. To each their own!
