12 Cups water
Heat equal parts of oil and flour. Continue to cook the mixture down stirring frequently until the mixture has the color of peanut butter. The darker the roux the darker the gumbo. DO NOT BURN THE ROUX .
Combine water and chicken in large pot. Bring to boil. Reduce heat and simmer until duck is tender, about 1 hour. Using tongs, transfer duck to strainer and cool, saving cooking liquid. Remove all meat from bones in pieces. Reserve the liquid.
Add the onions to the cooking roux until soft.
Add 8 to 10 of cups reserved duck cooking broth, andouille, tomatoes with their juices, bell pepper, celery, garlic, bay leaf, salt, thyme, basil, cayenne, and pepper. Bring to a boil. Stir in the roux mixture and cover partially and simmer until thickened, about 1 1/2 hours.
Spoon off any fat from surface of gumbo. Add file powder to gumbo and simmer 15 minutes. (If preparing ahead, cover and refrigerate. Bring to simmer before serving.) Mound rice in shallow bowls if desired. Ladle gumbo over and serve.