Hi Antti
> likely without the tube as they worked all the way to the end upside down in those cold temperatures.
Likely. Cutting an empty open will confirm. Interested in what you find.
> I'll sacrifice one half-used can just to see about the dust issue.
Very interested in what you find. Yes, I had very bad experiences with one Chinese brand. I returned the canisters to the shop in a bad temper, and they did not argue … :-)
> putting it underwater and piercing it there as this should eliminate the sparks.
I use a Ti tent peg driven into the middle of the valve to break the valve mechanism inside. The Ti does not spark. Works fine for me.
> if I do this correctly, the escaping gas should bring the dust into water and leave it there, right?
Seems right to me.
> Which way should the hole be pointing for max "dusting"? Down?
Seems right to me.
An alternate method is to use the canister upright to the end, then cut it open and look inside.
Another is to run the canister upside down but through a very fine filter. Need the right gear for that though.
Cheers