Place your leftover chicken scraps in an 8-quart stockpot. Add in the remaining ingredients (if the celery or carrots seem too long, cut them in half crosswise).
Fill the pot with cold water until everything is submerged; I don't really measure how much water to put in, though I do fill it to the 7 quart line.
Bring to a boil over high heat and immediately reduce the heat to a gentle simmer.
Let cook for 8 hours. Skim off the foam that rises to the top in the first hour or so.
When the 8 hours are up, strain the stock through a fine mesh sieve and discard the bones and veggies.
Refrigerate the stock overnight and remove any solidified fat from the top. At this point, you can either store it in the fridge for up to a week or freeze it for up to three months!