What is the best way to prevent condensation in fuel tanks?

Filling each tank after every flight is the optimal approach to prevent condensation in fuel tanks. When a fuel tank is partially filled, there is empty space that can allow moisture-laden air to enter as temperatures change. As the air cools, the moisture can condense and form water within the fuel tank, leading to potentially significant issues such as fuel contamination or corrosion.

By filling the tanks completely, you minimize the volume of air above the fuel, thus reducing the potential for condensation to occur. Additionally, a full tank limits the amount of air that can expand and contract, further decreasing the chances of moisture entering the tank.

While other methods might mitigate moisture issues to some extent—storing tanks in a cool place, using de-icer additives, or sealing tanks—none are as effective as consistently ensuring tanks are topped off after each use. Sealing tanks can prevent outside moisture from entering, but this does not address moisture already present in the air trapped inside a partially filled tank. Using fuel additives can aid in managing water, but they don't prevent condensation from forming if the conditions are right.