Put everything, except the salt, in a HUGE stockpot (12-quart minimum) and pour over the water. Cover the pot and bring to a full rolling boil. This could take almost an hour.
Once boiling, uncover, stir in the salt and reduce the heat to medium-low or low to get a gentle simmer. Simmer uncovered for 4 hours.
Once its done simmering, you could plunge the whole pot into your kitchen sink (if metal), insulated cooler or laundry sink, which you should fill with bags-full of ice and cold water, being sure not to get any water in the stock. Or you can leave it to on the counter to come to room temperature before stashing the whole thing in the fridge (which could take up to another 12 hours).
Once cooled, strain out the solids through a cheese cloth-lined fine mesh sieve and put the stock in the fridge overnight. In the morning, skim off most of the fat and discard.
Use immediately, store in the fridge for 3 – 5 days or freeze, either in 1, 2 or 4 cup containers, for about 3 - 5 months.
-You can save the outer layers, skins, roots and tops of yellow onions and store in the freezer. Use these in place of the onions in the stock--just make sure you have about 1 1/2 pounds of them total.
-Don't be alarmed by the cooled stock looking very thick and congealed--that's the gelatin from the chicken bones and its presence is the mark of a very good stock!