Preheat oven to 425° F. Place turkey wings, neck and tail onto a foil-lined and sprayed baking sheet. Season turkey parts lightly with salt and pepper. Roast until lightly browned, 20-30 minutes (turkey does not need to be cooked through). Remove from oven.
Place turkey parts into a 4 to 6-quart slow cooker. Add onion, carrots, celery, peppercorns, bay leaf and parsley stems. Fill slow cooker with water. Place lid on slow cooker and set heat to low; let cook overnight (about 10-12 hours). Strain stock; discard solids. If not using stock right away for recipes or gravy, chill and store, covered, in refrigerator for up to 5 days or freeze for up to 3 months.
Makes 2 to 5 quarts of delicious turkey stock (depending on the size of your slow cooker)
*To crack peppercorns, place peppercorns on cutting board; using a small skillet, place skillet over peppercorns and press with hand on skillet to crack peppercorns.