Blanch pork neck bones and chicken in boiling water for 2-3 minutes. Drain and rinse well. Cut watercress into sections and blanch in boiling water for less than a minute. Rinse and drain well.
Place pork, chicken and the rest of the ingredients in the upper pot of a double-boiler. Add hot water.
Fill the lower pot with enough water; ensure that it will not overflow. Place upper pot into lower pot and simmer over medium low heat for about an hour until meat is tender. Adjust with salt to taste before serving.