I would counter that 'best and cheapest option' is just to keep it full of fuel
All the usual stuff which would be done for this problem has already been done so this is something new to me. Prestige suggested replacing the tank on the basis that there's a collapsed hose inside, but that's quite a large undertaking. I'm going to have to drop the tank on Big Red soon as she runs out of fuel completely randomly, but also appears to have a vapour leak on the top of the tank. I'd be quite keen to have a good look inside and see what potential hose issues there may be, but alas my calendar is full until the winter which doesn't help much
