In order to make the corned beef less salty, remove it from it's packaging, place into a bowl of water. Place the water in the fridge for 3 hours. You can skip this if you aren't worried about your corned beef being too salty.
Remove corned beef from the water. Pat dry.
Add the contents of the spice packet that came with the corned beef along with any additional spices you would like (see notes).
Vacuum seal the corned beef.
Add to a 152 degree water bath. Set to cook for 24 hours.
Make sure the waterline stays about the minimum line for your sous vide machine. Covering with foil will help keep water from evaporating.
After 24 hours carefully remove the corned beef with some tongs. Cut open the package and move the corned beef to a cutting board.
Slice the corned beef against the grain and serve.
Refrigerate leftovers and try to use up within 3-4 days.