A 500mm length of hose that will fit into the small hole in the filler neck, insert hose with a hose click on connector fitted, (just push hose on connector)
Push hose all the way into filler neck so the connector rests against the base of filler.
To fill, simply enter hose with a clip end into filler hole & push onto connector untill it clicks, turn tap & fill.
To remove withdraw hose & connector just far enough to release the clipon, push joiner & hose back into filler ready for next time.
I built one similar only added a small plastic tap out of the AG section at Bunnings to let me control the flow at the filler when the pressure is to high.