Disposing of old curing salt?

[Vermis]

After searching through old topics here, I'm guessing my five-year-old cure #2 in a badly-sealed jar isn't much cop anymore. While I order some more, how do I get rid of the old stuff? Will it have broken down enough to be safe in the usual household rubbish, or is there a more complicated procedure?

[wheels]

Personally, if it's not contaminated, I'd use it. But, if not, maybe the local chemist/pharmacy? They have loads of drugs to get rid of, so must be used to the problem.

That said, plenty of water and down the sink can't do much harm surely?