Prepare the Tamarind:
If using fresh tamarind, boil the tamarind pods in 2 cups of water for about 15 minutes until soft. Mash the tamarind in the water to extract the juice. Strain and set aside the liquid, discarding the seeds and shells. If using tamarind paste, mix it with 2 cups of water to dissolve.
Cook the Pork:
In a large pot, combine the pork and 8 cups of water. Bring to a boil, then reduce to a simmer. Skim off any foam that rises to the surface.
Add Aromatics:
Add the quartered onion and tomatoes to the pot. Stir in the fish sauce and green chili peppers. Let it simmer for about 45 minutes, or until the pork is tender.
Add Vegetables:
Once the pork is tender, add the daikon radish and eggplant first. Cook for about 10 minutes. Then add the okra and green beans, and cook for an additional 5-7 minutes until all the vegetables are tender.
Add Tamarind:
Pour in the prepared tamarind juice (or dissolved tamarind paste) into the pot. Adjust the sourness to taste. If you want it more sour, you can add more tamarind.
Final Touch:
Stir in the water spinach and cook for another 2-3 minutes until wilted. Taste and adjust seasoning with additional fish sauce or salt as needed.
Serve:
Ladle the hot sinigang into bowls and serve with steamed rice and extra chili on the side.