In article , aemeijers wrote:

OP is talking about the disposable small cylinders, like for a soldering
torch, not the refillable big ones for a grill. Like everyone else says,
if they are empty, just trash them.

I agree. If the OP is still concerned, he can always call his
local City Hall. They are generally VERY responsive and helpful
when it comes to "How do I properly dispose of..." questions.
In some cities, they might refer you to a utility company but
they're typically just as helpful on these matters.

Every time I've called in one of those questions I have
received instructions that were legal, safe, responsible,
and totally satisfactory to me in terms of cost/convenience.

Most cities and utility companies are pretty darn good at
this stuff.

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