Place turkey carcass in a large soup pot.
Add 8 boxes of chicken broth.
Bring to a boil; cover the pot, reduce heat and bring to a simmer and cook, covered, for about 5 hours over low heat.
Skim off any foam/scum that rises to the top.
Remove from the heat and, when the stock is cool enough to handle, strain through a colander to remove bones or unwatted turkey skin/fat pieces; ensure you reserve the broth and turkey pieces; after it has been strained, return the broth and turkey pieces to the pot.
To the broth and turkey pieces, add the carrots, celery, onion, rice and seasoning, if using.
Bring to a boil; reduce heat and simmer soup for about 1 hour or until wild rice and vegetables become tender.
This soup is soooo good. Hardy and filling and perfect for post Thanksgiving turkey leftovers.