In a large crockpot, drizzle the oil and add the chopped celery, onion, carrots, and garlic. Let simmer a bit until the veggies are warm and then add the chicken carcass, water, and parsley. Simmer on low for 10-12 hours. Strain. Stock can be used immediately or frozen.
Recipe by Five Wooden Spoons at https://www.fivewoodenspoons.com/2012/11/09/crockpot-chicken-stock/