In a 15-20 pound roaster or Dutch oven, heat 1/8 inch of oil. (Use more if crawfish tails do not have much fat on them.) Fry crawfish, a layer at a time, until they are crusty, not brown. Remove from oil and set aside. Saute' onions and bell peppers in oil until clear. Return tails to pot and stir in flour until smooth, adding more oil if needed for smoothness. Gradually add water to achieve consistency desired. Stir in shallots, parsley, and seasonings, and bring to a boil. Continue boiling rapidly for 10 minutes. Turn off, cool and refrigerate. To serve, reheat slowly and spoon over mounds of steaming rice.