Place pork into the ceramic bowl of crock pot.Pour enough juice and apple cidder vinegar into the bowl to completely cover pork, maintaining a 2:1 ratio of vinegar to juice. Add the salt. Place the bowl in the refrigerator and allow pork to marinate recommened 12 hours and up to 24 hours.
Drain enough liquid from the bowl until 1/2 inch of pork is exposed. Add onion to remaining liquid. Season exposed surface of pork with cumin, chili powder, and brown sugar. Place bowl into the base of crock pot and cook until pork is tender and falling apart easily. (6-8 hours)
Carefully remove pork from crock to cutting board; shred meat into strands. Before draining liquid from crockpot set about 1 cup aside.
Pour out remaining liquid, and place shredded pork back into crockpot bowl, mix in your favorite bbq sauce, using the reserved liquid to thin the sause. Set crockpot on warm to until ready to serve.