Here is the one we use for our whole hog (But can be used for Boston Butts as well)
Sorry we don't really measure
Apple Cider vinegar
Mix it all in a pot and bring to a boil, then simmer. What you want to do is let the vinegar cook down. Add it to the pork after the pork is ready to pull. Let the meat simmer in the vinegar sauce for a while. Enjoy. Search my threads and you can see how we simmer it for a whole hog.
Chargriller Duo Model #5050 w/ firebox, Homemade box pig cooker, Brinkmann Square Vertical Charcoal Smoker
If I have to pull up my big girl panties and deal with it one more time the elastic is going to break and I really will have to show my butt