In a pot over medium heat, combine pork and enough water to cover. Bring to a boil, skimming scum that accumulates on top.
Once broth clears, add tomatoes, onion, and fish sauce. Lower heat and simmer for about 1 to 1 ½ hours or until meat is tender, adding more water as necessary to maintain about 8 cups.
Add gabi and cook for about 4 to 6 minutes or until tender.
Add chili peppers and radish. Continue to simmer for about 2 to 3 minutes.
Add long beans. Continue to cook for about 2 minutes.
Add eggplant and okra and cook for another 1 to 2 minutes.
If using packaged tamarind base, add to the pot and stir until completely dissolved.
Season with salt and pepper to taste.
Add bok choy and continue to cook for about 1 minute. Serve hot.
If Using Fresh Tamarind
Wash tamarind and place in a saucepan with 1 cup water. Bring to a boil and cook until soft and outer skins begin to burst.
With a fork, mash tamarinds.
In a fine-mesh strainer set over a bowl, pour tamarind and liquid. Continue to mash with a fork, returning some of the liquid into the strainer once or twice, to fully extract the juice.
Discard seeds and skins. Pour tamarind juice into the pot of sinigang.
Video
Notes
For a clearer broth, you can parboil the meat. Bring to a boil, drain, and discard liquid. Rinse the meat and pot well and continue cooking with fresh cold water. Tend to the soup regularly by removing scum that accumulates on top.