In a large mixing bowl, combine the eggs, milk, bread crumbs, onion soup mix and sage and stir or whisk together until well combined. Add the ground beef and ground turkey and mix together (I recommend using your hands) until thoroughly combined. Transfer the meat mixture to a cutting board or other clean, dry surface and form into a loaf that will fit in your slow cooker without touching the sides. If you prefer, you can place a long, wide strip of aluminum foil into your slow cooker at this point before adding the meatloaf to help you lift it out at the end (I just used two spatulas to lift mine out).

Add your meatloaf to the slow cooker and cover. Cook on low for 6 hours or high for 3 hours until fully cooked. Remove the cooked meatloaf to a cutting board or serving platter. Spread the ketchup over the top of the meatloaf and slice into 12 even slices.