Place rice into a large container and cover with several inches of cool water; let soak 8 hours to overnight. Drain and rinse.
Bring 4 quarts water and chicken broth to a boil in a large pot. Add turkey carcass; bring back to a boil. Reduce heat to medium to bring liquid to a simmer; cover partially and cook, stirring occasionally and adding water as needed, until rice is partially dissolved, about 3 hours.
Season congee with salt and pepper. Discard bones before serving.
