[stephen low]

Greg

The tube does need to be connected somewhere.

The fuel filling assumption should be taken as wrong and there is always the chance of over-filling. Where does that fuel go, into your boot if not redirected.

The prior owners of my unfinished kit had bought the standard steel GF fuel tank. Beside the main fuel filling neck into the tank is a smaller tube to which my upper overflow pipe is connected.

Obviously both tubes and attached pipes will fill as you overfill the tank but the additional volume helps limit potential for complete overflow at the external fill point. As you say too, it allows air reventing back into the tank and no fuel escape into the boot by the connecting smaller tube.

If your tank doesn't have a second tube, you could direct the overflow tube to the outside world, then you don't end up with a boot full of fuel with all the risks and issues that will bring.

It's a must have ... not a desirable option!

Cheers

Steve