With respect to the gas if it is ethanol blend remove it before doing anything, if it is the MTBE fuel add stabilizer and octane booster, fill the tank with fuel if you are sure there is no water. Since the tank was not filled it most likely has water in the fuel, its up to you if you want to take a chance.
What is involved in fogging down the engine? If storing the boat for a while, what is the best way to leave the tank? Full? Drained fully? How long can it be stored for each?