I always used to do it, but read something from Maine Cat expressing the view that if there's less fuel in the tank, there's less capacity to absorb water so you can start the next year with fresh fuel. He wrote that air volume in the tank doesn't change how much water the fuel can absorb. Makes sense. I tried that two winters ago and even though I treated with Bio-Bor, I started to get clogged fuel filters in Spring (never had that before).

I emptied the tank into 5-gallon jugs and filtered it all with 2-micron filters. PITA. I will leave my tanks topped off and treated with Bio-Bor from now on, as in the past.