I can tell you one thing...veggie oil is a pain to get off!!
I have a deep fryer, and after about 8 years of use, I wanted to give it a VERY deep cleaning. I always washed it out with dish soap whenever I changed the oil in it, but over the years it had developed a very hard crust above the oil line. over the course of 2 weeks, I would spray it with oven cleaner with lye, let it soak then scrub it steel wool. it was still a very difficult and took a lot of effort.
but I would NOT do that with a gun, unless you planned on getting it refinished, AND as long as it had no aluminum parts.