In the turkey roasting pan (which should not have been cleaned!), add back in the turkey fat. Sprinkle in the flour and whisk into the fat until it's all worked together into a paste. If paste is too thick/clumpy, add in a little more grease. If it's too greasy, sprinkle in more flour. Whisk and cook the roux over medium-low heat until deep golden brown.
Pour in the chicken broth, whisking the whole time. Allow to cook and thicken for several minutes, whisking occasionally. If the gravy gets too thick, or if it's too salty, thin it with a little of the giblet water. If the gravy is too thin, just keep cooking it until it thickens up.