BTW, by DOT rules you aren't supposed to transport refilled disposable canisters. Just because they make an adapter to refill them doesn't mean it's a great idea. The metal gets stressed each time they're filled and they're only designed to be filled once. Plenty of people do it though. 

Anyway, you can punch a hole in them (big nail or screwdriver and a hammer) and then they can be scrapped as "mixed metal" or around here some places call it "tin". 

A better idea to eliminate this problem is to buy refillable canisters, they come in several sizes, or buy an adapter to use a 20 lb tank (like your home bbq grill uses) to attach to your portable grill.

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