We are not trying to insult the way you burn your fire.
My comment on having a fire problem was explained away when you said you flood the pan and then warm it with a medium pine fueled fire.
My thoughts on cleaning the bottom to a shine are that it will only look like that until your first fire of the next season. If you brush the bottom and keep the pans dry any soot that remains will not harm the SS. I have never heard of anyone cleaning using walnut hull media (but I used to use it to polish brass ammo cases in prep. for reloading, I now use SS media in a tumbler for that).
In your original post you say that you think if you could get the pans truly clean on the underside that you might be able to keep it clean using your power washer. Does that mean you would wash it daily in place, I think not. And a full season of regular burning, if you keep flooding the pans and warm them with pine but not to a hard boil will get you back to the same as what you now have. I say, if you want to persue it, put water in your head tank, fire the evaporator to a hard boil for 30 minutes and then let the fire burn out. I then think the bottom will brush clean without any pressure washing or oven cleaner or blasting with walnut hull media or beads.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.