Get perfect 'low and slow' pulled pork sandwiches every time, the easy way, in a slow cooker...
Alternately, you could smoke the butt for 3 hours or so, then transfer to the slow cooker and finish up using this method, very few would notice the difference.

Here is what you will need:
SAUCE
1 Cup Finely Chopped Onion
2 Cups Apple Cider Vinegar
6 Ounces Tomato Juice
1 Tablespoon Black Pepper
1 Teaspoon Garlic Powder
1/2 Teaspoon Chili Powder
1 Teaspoon White Sugar

DRY RUB
2 Teaspoons Brown Sugar
2 Teaspoons Coarse Salt
2 Teaspoons Paprika

1 Large Sweet Onion
5 or 6 Pound Boston Butt

Start out with the sauce; puree the onion in a blender with around 1/4 cup of water, then transfer to a saucepan. Add some additional water to cover, bring to a boil, then reduce to a simmer and cook, stirring continuously, until nearly all water has evaporated. Now add your cider vinegar, tomato juice, black pepper, garlic powder and chili powder. Return to a boil, then mix in the sugar and remove from heat to cool.

Next, mix your brown sugar, coarse salt and paprika into a dry rub and apply to all sides of the boston butt. Quarter the onion and place the pieces on the bottom of the slow cooker, then put your roast on top of that and pour in about 1 cup of the sauce made earlier (save the rest for next time or use as a sauce on your sandwiches). Turn the crock pot on low, and let the roast cook for at least 8 hours, then check for tenderness. Expect 10 to 12 hours total cook time before the meat will be ready to pull (fork tender).

Remove the meat and onions from the crock pot and allow the pork roast to cool a bit. When cooled enough to work with, pull the pork into fine threads using two forks, or your hands. It is just that simple, make a sandwich with some of the vinegar based sauce we made, or with your favorite BBQ sauce, which is how we like it.