Place the pork in your slow cooker, fat side up. Rub with garlic and top with onion (no liquid is necessary). Cook on low for 9 to 10 hours, or until the pork pulls apart fairly easily. Remove to a platter to cool. Once cooled, pull the pork apart and place in a large skillet (or Dutch oven).
Prepare the sauce: Combine all of the sauce ingredients in a saucepan. Bring to a boil over medium heat. Remove from heat.
Add the sauce to the pork. Stir in the lemon juice, vinegar and Tabasco (to taste). Cook over medium heat until bubbly, or place in a 375° oven for about 25 minutes.