id still question the reliability of the motor for actual transport reasons but to answer the question, the HF motor like most small motors is gravity fed meaning keep the tank above the motor and gravity will pull the fuel down to the motor. works well with bikes as the tank is in front of the rider, above the motor, and doesnt work well with cars since they usually have the tank below the cabin or in the transmission tunnel.
in your case, you should be able to swap the tank with any other gravity fed one (get a bike one, it's already made the right size and shape), all you gotta do is match the fuel line to fit the motor and the tank.
stay away from boat tanks and fuel cells since they will probably require a fuel pump of some kind.
also, put a good silencer on that thing, i'm sure you're well aware that it's not the quietest thing out there. otherwise everyone will run out to see why someone is riding a lawnmower to work.
