If I have to do it I make sure it is outside and i use a spare fuel hose with the ends removed and then pump with the bulb then siphon between containers making sure not to overfill. The transfer is quite slow but avoids spills. Pouring petrol at sea is not a good idea.
As your new boat has an outboard I would just purchase a second fuel tank or uf you are talking about fueling the small internal tank it would be very dangerous. Most with internal tanks except the real small hp ines have the ability to connect an external tank as well. Buy a 30 ltr external tank will be plenty.
