Place pork in a large stockpot. Cover with water. Add 3/4 c. of vinegar, onion, garlic and peppercorns. Bring to a boil. Reduce heat and simmer, partially covered. Skim froth and add water as needed. Cook for 60 minutes.
Preheat oven to 350F. Transfer pork to a rack in a roasting pan. Pour 1/3 c. vinegar over pork. Roast 45 minutes, turning every 15 minutes. Transfer to a plate and let stand until cool enough to handle.
Reheat BBQ sauce.
Pull pork into shreds. Place into hot, sterilized pint jars. Ladle sauce over the top to fill the jar and fully cover thte meat. Leave a 1 headspace.
Process, following your canner's instructions, for 75 minutes in a pressure canner at pressure listed for your altitude.