... If water forms in the tank, it's going to the fuel filter. It has no choice since water is heavier than diesel.
My fuel tanks are vented. My fuel cans are not. Wet outside air can enter the tank when warm and drop moisture as it cools. The fuel cans not so much. They do squeeze down as it cools, and if I were to vent them on a warm, moist, day they would get water inside. I don't, so they don't.