I agree with everything Pitlamp says. However, if you are diving with other CDG members from time to time, you can of course get a fill if they are going to the compressor.
Diving with other experienced divers is by far the best way to learn to cave dive. I learnt a hell of a lot just carrying for other divers. Just seeing how they prepare for a dive is very important, because the success or failure of a dive depends just as much on all the preparation as on what you do once in the water.
Mark