How to complete eradicate peanut oil (deadly allergy)

I registered just to post this and ask for help. We own a very old, very large cast iron pot that we use at the lake to make popcorn over the fire for about 50 people during our annual extended family get-together. Last year, we accidentally used peanut oil and one of our family members is deathly allergic to peanuts. He nearly needed to be hospitalized.

We need to completely clean the cast iron pot to remove all traces of peanut oil, and I was hoping this forum might be able to assist with some advice. It doesn't matter how harsh the cleaning method needs to be, but we absolutely need to make the pot safe again.

What would you recommend?

I would try a lye bath, perhaps double strength. Normally 1 lb. lye crystals per 5 gallons is used, but some go twice that without any issues. Since it's the grease and oils in the build-up the lye reacts with to clean, that would seem to be a logical choice. Perhaps follow it with a scrubbing with Dawn dishwashing liquid, also known for grease dispersal. If the pot is very large, you could mix up the lye solution in the pot itself, but that could be a bit tricky. The pot would need to be mostly filled with water, the lye added and dissolved, then the pot topped up to the lip with more water. It would need to be done outdoors, obviously, and kept away from people and pets for a few days. If it could fit in a large trash bag, the oven cleaner spray and bag method would allow you to treat it inside and out. Of course, given the circumstance, you would absolutely want a way to test if it was effective, but I don't know what that would entail.

Recommended methods for lye here: http://www.castironcollector.com/cleaning.php#lye