Prepare pit for clambake. Peel husks off corn; remove silk. Put 1 inch of water in a 30- to 40-quart stockpot. Place lobsters in pot, followed by onions, corn, potatoes and clams. Cover pot and place on rack in pit. Let water come to a boil (about 30 minutes). Cook with water boiling for 30 minutes or until potatoes are tender. Remove pot from fire; place food on large platters. Serve with sauces.