In a large saucepot, bring the 8 cups of water to boil. Mix tamarind paste with the 6 tablespoons of hot water and strain through a fine strainer. Add 4 tablespoons of the strained tamarind paste, the sugar, 2 tablespoons of the fish sauce, the pineapple, tomatoes, and celery; cook for 3 to 5 minutes. Add chicken and cook until chicken is done, about 10 minutes. Taste soup and add more of the remaining 2 tablespoons tamarind paste and fish sauce, if desired. In a small skillet, heat oil and fry shallots until golden brown; drain. To serve, place bean sprouts in serving bowl; add soup. Garnish with shallots, basil, and chili peppers. Makes 4 servings.
*Zuiki taro stem is available in Asian grocery stores or Chinatown.