I am making a simple coffee-making kit for daytrips, using a tin can suported by a home-made alcohol burner. Everything fits neatly into the tin and a lid is pushed on. Total weight should be around 4oz.
I am using a tin which contained grapefruit slices, and I've washed it and filed it down etc. But the tin can has started going rusty after leaving water in it overnight. Should I be treating it with something, or would a different type of tin work better?