I like more flavor, in an injection, than just au jus, so I use my own!
DM's Brisket InjectionI don't always inject, but if I do, I do it this way:
1. Trim the brisket, and give a dusting of Morton's TenderQuick for 15-30 minutes (wrapped in the fridge).
2. Rinse thoroughly, and pat dry.
3. Coat in mustard, add rub, and wrap in plastic for the fridge, for an overnight rest.
4. Remove, and into the smoker @ 225°, with 6-7 oz of wood of choice. For me, that's hickory, mesquite, white oak or red oak, or a mixture of hickory and one of the others!
5. Start checking the feel of it around 190. It should be loose, floppy, if you pick it up in the middle. If you stick your finger, or a toothpick, in it, it should go in like warm butter! I've learned from Brian (Pork Belly) not to get wrapped up on internal temp of a brisket..."feel" is important!