1. Go to the supermarket and buy two bottles each with 6 liters water. 2. Empty the bottles in front of the supermarket. 3. Go to the fuel station. 4. Buy 11 liters of diesel. 5. Go back to the boat and fill the 11 liters into the tank. 6. Repeat step 4 & 5 many times. Result: The guy from the border control in the harbor is your enemy but the guy from the petrol station is your best friend.