Crock Pot Pork Roast with Sauerkraut and Apples

butter

2.5-3-pound pork loin (loin, tenderloin, or sirloin)

kosher salt and freshly ground black pepper

/jar of sauerkraut, undrained

maple syrup

packed brown sugar

brown or mild coarse grain mustard

medium onion, chopped

medium apple, sliced