How to fill an outboard fitted with an integral fuel-tank (especially those in awkward positions) without spills.

Fit a commercial twist valve - or similar - to a fuel jerry can. This has a stub to which is hose-clamped a clear plastic fill-hose sized to reach the motor's gas tank from inside the cockpit. The valve also allows an easy means to close-off the can for storage.
To make an automatic shutoff, attach tubing to the jerry can vent and arrange it so that when gas in the tank reaches the desired level the vent tube becomes blocked. This stops the flow immediately.
Ensure that the tubing is suitable for use with gas (petrol). Attachment of the tubing depends on the can used. One method is to drill a suitable hole in the vent cap and push the tubing through. Ensure that any existing vent (if any) is sealed, as the stopping of the fuel flow depends on air-tightness.
Attach the tubing to the fill-hose at several places as shown in the diagram.
At the gas tank end of the hose affix a hose clamp that is sized to be too big to fit into the gas tank to act as a stop when pushing the fill-hose into the gas tank. The distance from the clamp to the end of the fill hose therefore sets the fill level. Cut the fill hose diagonally at the end to assist in draining off the last few drops of fuel after the flow has been shut off.
Colin