To make the sauce: Place the tomato sauce, ketchup, cider vinegar, brown sugar, and garlic powder in the crock pot. Stir until mixed. Season both types of pork with 1/4 teaspoon salt and 1/8 teaspoon pepper and add to the pot. Top with onion and lightly stir.
Cover and cook until pork is fully cooked, on high for 3 to 4 hours or on low for 7 to 8 hours.
Remove all the pork and place it in a large bowl. Shred each piece using 2 forks: one to hold the pork in place and the other to scrape across the meat and shred it. Return the shredded pork to the crock pot and mix well with the sauce.
If you're serving a group, keep the crock pot on its lowest setting, so the pork stays warm. Season with crushed red pepper, if using. Yum time!
Alternatively, recipe can be baked in a preheated oven, covered, at 325 degrees F for 3 to 4 hours.