Mix the salt, thyme and black pepper together. Massage the mixture into the legs and wings. Make sure every part has some on it. Vacuum seal or put into a sealed container and refrigerate overnight, or up to a few days.
When you are ready to cook, rinse off the legs, then dry well. If you are vacuum sealing, make sure the legs are not stacked. They need to be in one layer. Divvy up the fat into the bottom of each vacuum bag. Divide up the bay leaves into each bag. If you are not vacuum sealing, put the bay leaves in the pot of fat.
Get a large stockpot mostly full of water and bring that to a bare simmer, a shimmy, really. Set the sealed vac bags in the water and cook at about 180°F for at least 3 hours, for store-bought ducks, and 6 hours or more for wild geese. The cooking time is about the same for the traditional method, which I do in an oven-proof pot in a 200°F oven.
Remove the bags from the water and plunge into an ice water bath to cool. Remove them to a rack to dry, and when they're dry on the outside, store in the fridge for up to a month.
To eat, you can shred the meat and use it that way, or eat whole and cold (a very good duck blind snack!), or crisp up the skin in any of the ways mentioned above.