Does anyone have first hand experience with these and can explain exactly how these work? I understand how to put the fittings together, but nothing else.

Thanks!

I don't have first hand experience, but I believe the end pushes up in to the fitting when it's put on the "filler neck" to allow the fuel to escape. However, unless that handle is also a vent, I don't see how this would work at all. I tried searching for the Nixon Prosport as well as youtube and google for how these things work and apparently it is secret. I can only suggest finding another nozzle like the one on your car and install it in a board or something. Then fill one jug with water and just practice.