Put the pork in the large soup pot. Fill with water to the point that it over the pork. Bring it to a boil, then let it simmer for ten minutes. Remove the pork, and discard the liquid. This will clean the pork. Rinse the pot, then return the meat. The pork should be covered with water that is fresh until it covers the meat. Bring the water to a boil.
Add the onion, and cook until 1.5 hours. Be sure to check every 30 minutes for any impurities. Scoop away any you see.
As the soup simmers while the soup is simmering, mix 1 cup of water and tamarind in a small pot. Bring it to a boil and allow it to boil for a while until the tamarind dissolves.
You could accelerate this process using spoon's handle in order to break the tamarind. Put the crushed tamarind in the fine mesh sieve and into an ice-cold bowl. Set aside.
Once the soup has simmered for 1.5 hours After that, add the ginger and pineapple into the soup. Let it simmer for another 20 minutes.
Add the catfish to the pan and let it simmer for ten minutes or so until cooked to perfection.
Finally, add the vegetables and the tamarind from step 3. Let the soup come to a simmer and serve it with white rice. Be sure that you taste the soup for the seasoning, and add salt if you find it bland.