Cook on low heat for 10-16 hours. It's handy to set it going late the night before.
An hour or so before serving, get out two large bowls and a small one. Turn off the crockpot. Separate into: (1) skin, fat, and bone, (2) onions, (3) meat, and (4) broth. Discard the skin, fat, and bone. Dice the onions. Reserve the broth for later. It's great as a base for rice or soups. Refrigerate it, remove the excess fat once it has cooled, and you can freeze the (gelled) broth. Place the meat in a big bowl as you separate the contents of the crockpot. Once you have all the meat, take two big forks and shred it. This process should take all of 2-3 minutes; the meat will be very tender and will separate easily.
Place shredded meat, diced onions, and BBQ sauce into the crockpot and mix well. Heat on high for 30 minutes and serve.
It's traditional to serve pulled pork with shredded cheese and cole slaw, but there are lots of other ways to use it. Leftovers are great in egg rolls (!) or can be reheated with a microwave. It will last in the refrigerator for a week.