Rinse turkey legs and pat dry. Season with poultry seasoning, salt, and pepper. Wrap each leg tightly in aluminum foil.
Place wrapped legs into a slow cooker with no liquid or other ingredients. Cover and cook on Low until meat is no longer pink at the bone and the juices run clear, 7 to 8 hours. An instant-read thermometer inserted near the bone should read at least 165 degrees F (74 degrees C).
Remove from the slow cooker and let sit for 10 to 15 minutes. Carefully remove and discard foil. Separate thighs from drumsticks.