Also, in the early days, I was told to be very careful that you didn't lose any of that magical pixy dust known as ether. Somehow, your fuel could go stale and you would never, ever be able to start your engine on that fuel again. Never ever. You had to bless it with the addition of the ether that was obviously lost.
This is an interesting one. I've always tried very hard to preserve my highly volatile magical pixy dust, just as Andy says. Yet recently, I was at a friend's place in Brisbane and dragged out a PAW 249DS-powered model that we'd been flying this the previous week. On the off-chance that there were some dregs left in the tank, I choked it through a couple of times and flicked it. It fired instantly, and ran out the dregs.
Now this was a small quantity of fuel which had been sitting for 8 days in an unsealed tank, in a location where the daytime temperatures were up around 30C. By rights, there should have been no ether left and nothing much should have happened when I flicked it. Yet it fired and ran as if the fuel was freshly made. Fuel for thought, eh (so to speak)!