I don't know about potatoes helping flue pipes and chimneys, but for some reason this reminded me of when I was a young teenager and my dad took his high carbon steel hunting knife (not stainless steel) and stuck the blade in a potato. A few days later he removed it, and it had a nice mild and mottled bluing on it that reminded me of the receivers on some old lever action rifles. It has never rusted. I still have it.
Edit: The second knife photo seen at this linked website reminds me highly of the finish that the potato gave the blade. A forced 'patina" bluing I guess is what my dad achieved.http://www.thetruthaboutknives.com/2014 ... bout-rust/
Perhaps burning potatoes can also do this to the inside of the flue pipes?