In a large saucepan combine the neck and giblets, the broth, the water, the celery, the carrot, and the onion and bring the liquid to a boil, skimming the froth. Add the bay leaf, the thyme, and the peppercorns, cook the mixture at a bare simmer for 2 hours, or until the liquid is reduced to about 5 cups, and strain the stock through a fine sieve into a bowl. The stock may be made 2 days in advance, cooled, uncovered, and kept chilled or frozen in an airtight container.