candy or tea tins for pots?

If it is actually "tin" rather than aluminum – beware. It will not weather well, and you will have extremely large amounts of metal contaminants in your water. Most tins like you mention are food grade, which means the tin plating over the steel will not rub off on your food… but that's not considering adding heat and liquids. Over time (and likely not much time) the heat applied will cause a separation of the tin plating from the steel underneath. As soon as that happens, you'll have rust everywhere.

But then, maybe it's aluminum. Distinguishing between the two can be awfully difficult. I suppose, if, for $0.50 you can get another you might want to cut it or drill some holes through it and submerge it. Let it sit outside for a while an see what happens.

My stove was made out of this kind of thing. It rusted eventually.

I recently bought some salt that came in one of these tins. The tin was lined with plastic as I imagine the salt would corrode the metal. In fact, it already was corroding the lid shortly after opening the tin.

It's not that hard to tell the difference between stainless, tin plate and aluminum. However, it is hard to explain how to tell the difference. It's tinned steel if you can pick it up with a magnet. If it's not strongly attracted to your magnet, go to the store and find a stainless steel pot and an an aluminum pot. You will note the difference in color and luster and should be able to identify your can from there.

As for toxicity of tin plating, I don't think it's toxic. Solid copper pots are plated with tin on the inside to prevent toxic copper from contaminating the food.

H