I use Knorr's beef gravy mix. i mix up a very thick batch. I inject from the sides of the meat with the grain. I have a Spitjack injector so it is big enough to go 3/4 of the way through even a good size brisket. As I inject I slowly move the needle out to keep from having pockets of injection. Massage the heck out of it when you are done and then let it sit in the fridge for around 6 hours and you will be good to go.
Meadow creek BBQ42, Kamado Joe large, UDS, Yellow Thermapen, Gasser