lurker:Can I refill my can at the Petrol station?
I clean mine out twice a year with my compressor, I would suggest a water trap might be a good idea depending on the compressor.
Otherwise you may get water in the mix from condensation inside the tank etc.
Also, something I haven't tried but am going to (which may be completely unsafe), on Youtube there are videos showing you how to refill your cans with a compressor.
The cans are still useful to have on your desk for quick tidy-ups of your keyboard etc, but pricey if you keep buying them.