In a small bowl, whisk together the ketchup, garlic, apple cider vinegar, brown sugar, molasses, honey, water, Worcestershire sauce, and paprika. Season with salt and pepper to taste.
Stir in the minced onion.
Transfer the mixture to the slow cooker.
Add the pork, turning to coat it in the barbecue sauce mixture.
Set the slow cooker on low for 4 - 6 hours until the pork tenderloin is fork tender.