Preheat oven to 350 degrees F (175 degrees C). Rinse turkey and remove giblets. Salt and pepper to taste. Sprinkle the bottom of a turkey size oven bag with flour. Place turkey, celery and onions in the bag. Seal bag and poke several holes in it with a fork. Bake 3 to 3 1/2 hours, or until internal temperature of the thigh meat reaches 180 degrees F (85 degrees C).