1Slice onion and place on bottom of the slow cooker. Pour one cup of water on onions. Rinse roast and place fat side up on onions. Pour 1 can of root beer over roast. Combine seasonings and rub evenly on roast. Cook on low for 6-8 hours depending on size of roast and desired tenderness. Roast should be fork tender. Once roast is cooked let cool enough to handle and shred with fingers. Place pork back in slow cooker set on warm.
Combine pan drippings, bbq sauce, 1 can of rootbeer in a large sauce pan, whisk to combine completely. I use all of the pan drippings but if I have less than a cup I make up the difference with chicken stock. Bring sauce to a boil stir, then turn heat down to a simmer. Cook until sauce has reduced by about half. Sauce should coat the back of a spoon well. You can add water, soda or bbq sauce to thin sauce if needed.
3Pour desired amount of sauce over pork and stir to coat meat completely. I serve the meat on hamburger buns or sesame seed buns from the bakery.
4If using a larger roast all ingredients can easily be doubled or tripled if needed. You will also need to cook roast longer.