Prepare the Brussels sprouts: Rinse and cut off the end of the Brussels sprouts. Cut them in half or quarter them if yours are big. Place them in a vacuum-seal bag, and add the bacon and the reserved fat with garlic. Arrange the Brussels sprouts in one or two layers in the bag for even cooking. Vacuum-seal the bag.
Sous vide the Brussels sprouts: When the water reaches the desired temperature, submerge the Brussels sprouts and weigh them down with a heavy, heat-proof object like a rack or a pot lid. Set the timer for 1 hour.