In a large pot, combine 2 qt of water with catfish bones, bring to boil then simmer for 30 minutes.
½ lb catfish bones
Discard the bones, strain the soup through a fine-mesh sieves. Pour about 1 cup of the soup to a small mixing bowl, then add tamarind soup base in. Stir to dissolve it completely, about 2-3 minutes.
4 tbsp tamarind soup base
Return the rest of the strained soup & tamarind mixture to the cooking pot. Bring to boil. Then lower the heat and add fish sauce and sugar, stir until sugar completely dissolved. Adjust the taste accordingly by using salt and sugar.
2 oz fish sauce, 2 oz sugar, salt & sugar
At this point the soup base can be kept under refrigeration for 2-3 days or in the freezer for up to 2 weeks.