Blanch duck and pig's tail separately in boiling water for 4-5 minutes. Wash the preserved salted radish well, then soak in water to reduce the saltiness. Cut into sections. Cut Chinese yam on the slant into thick slices.
Combine all ingredients and hot water into a large saucepot. Cook to a simmering boil for an hour or until meat is tender. Adjust with seasoning to taste.