Using a home-style meat grinder, alternately grind Boston butt, liver, green onions and parsley. Season ground ingredients with salt and peppers. Place the mixture into a large mixing bowl and add cooked white rice, water, and pimentos. Using both hands, blend until all is incorporated. Using a sausage stuffer, fill the casing and twist into 6-inch links. Place boudin links into a home-style steamer, cover, and cook 45 minutes or until sausage is firm.