Ah. I’ve used the champagne cork, and found it, as do you, to be a service item! I think that I’ll try a plastic float tied to the arm with something like tape, if I can find one which doesn’t bleed in ethanol/petrol.
Whilst on the subject (nearly), I took the petrol pipe out of the tank (of the “new” car) and found it completely blocked with gunk. I disassembled it, cleaned it and replaced it- ran a lot better. The car’s previous owner hadn’t used it for about 12 years, so it wasn’t ethanol! I