To make the stock: Dump the turkey or chicken bones and neck into a soup pot large enough to be able to hold at least 3 gallons of liquid. Toss in one large onion, the carrots and celery, and fill the pot with 2 gallons of water. Add in the peppercorns and a handful of parsley. Bring the pot up to a boil and then drop it back down to a simmer, let it cook for a minimum of 20 minutes. Strain out all the veggies and bones, and reserve the liquid. Congratulations, you just made some good turkey stock!
While the stock is simmering, chop the garlic, bell peppers, remaining onions and celery for the gumbo.
Preheat another large pot over medium heat with 1 cup of oil. Add in the flour and stir constantly, letting the flour mixture cook for about 10-15 minutes or so. Keep stirring or else it will burn, and you'll know if its burnt because it will stink to high heaven. If you burn the flour mixture, you have to start over. (Now it is time to open that beer that is listed above. It's not for the gumbo, so drink up! By the time you're done drinking your beer, the roux should be the color of the penny. The flour mixture will go from vanilla to beige to caramel to dark caramel color.)
Splatter Warning - Along with random splatter from stray veggies, you may get a major steam up when adding things to the pot that can be pretty painful to bare skin. The hot roux can be pretty fearsome as well, so long sleeves are highly recommended!
As soon as your roux changes from a light caramel to a dark caramel color, toss in the chopped vegetables. Keep stirring until the onions become translucent and soft, about 5 minutes. Add in that wonderful stock you made earlier, but only enough to cover the softened veggies. Give everything a good stir! Dont worry if the roux separates from the vegetables and looks a little sandy, it'll all come back together.
Add both of the cans of tomatoes including the juice, the sausage, salt, black pepper, cayenne, bay leaves and the rest of the stock. Make sure there's still room in the pot for the pulled turkey you'll add to the gumbo later! Bring to a boil then reduce heat and simmer.
While the pot is simmering away, heat a large, nonstick skillet over medium heat with a little bit of oil, about 3 tablespoons. Add the okra to the skillet to heat it up. The okra will shed a slimy-looking substance. Keep stirring until it starts to dry up -- about 10 minutes -- but just be aware that it won't go away completely. You're just trying to cook it out of the okra so it doesn't smear your gumbo.
When the okra is done, add it to the gumbo pot and quickly bring everything back up to a boil. Reduce the heat and simmer. Taste and decide whether you need to add more spices. Add turkey or chicken meat to the gumbo and let it simmer until heated through. At this point, the gumbo is basically done but it will only get better the longer it cooks down.
If you want cook it down or won't be serving it right away, be careful adding spices because it becomes more concentrated as it cooks down and hold off on adding the turkey meat until youre ready to serve it so it doesn't disintegrate on you. If using a brined turkey, it's better to err on the side of caution and withhold extra spices altogether.