Place the trivet in the Instant Pot, over the leftover juices from the whole chicken, and place chicken carcass on trivet
Pour water into the pot, and add sea salt and celery stalks
Place lid on Instant Pot, and turn valve to Sealing position. Hit PRESSURE COOK for 60 minutes
Pot will take a few minutes to pressurize, then it will start counting down and cook for 60 minutes. Allow a 10-minute release (or longer, or full natural release if you want) then do a quick release or gradual quick release for remaining pressure to drop. Hit CANCEL to turn pressure cooker off
When pin drops, open lid, carefully lift trivet (wear hot mitts), and discard chicken carcass. Pour stock through mesh strainer into a bowl, and separate into smaller containers to refrigerate or freeze
Stock should gel when refrigerated. You can skim off the top layer of fat easily and discard before using, or you can use fat in place of oil or butter if making chicken soup