Combine the sugar, rice vinegar, soy sauce, fish sauce, lemongrass, ginger, garlic and water in the bottom of a slow cooker (ideally a similar width to the piece of pork). Stir together to mix and to help the sugar dissolve.
Add the pork and turn so a bit of the cooking sauce sticks to the top of the pork, then cook on low for 6-8 hour until the pork is fall apart tender.
Notes
If you'd like to serve this as I have here, you'll need approx ¼ cup uncooked rice per person (I used brown for texture), cooked per packet instructions. Make quick pickles as in my banh mi soft shell crab sandwich (here I just made with carrot rather than part daikon) and then add a handful of salad leaves with a few cilantro leaves on the side and slices of cucumber.