Fire up smoker to 225°F (107°C). While it preheats, prepare brisket.
Heat up a small saucepan over medium heat. Combine all injection marinade ingredients until fully dissolved.
Place brisket in shallow baking tray. Load meat injector with marinade. Insert injector perpendicular to meat grain direction. Inject in a grid pattern across the meat, with an inch between each hole. Save half of the marinade to use later.
Mix all rub ingredients in a small bowl. Apply liberally to meat, covering all sides in an even coat.
Place brisket in smoker, fat-side down on the grates. Smoke for six hours.
Remove brisket from smoker and place on a sheet of aluminum foil. Drizzle the remainder of the injection marinade over the meat. Wrap tightly in foil, eliminating any pockets of air. Double wrap for good measure.
Increase cooking temperature to 275°F-300°F (135°C-149°C). Place wrapped brisket back on smoker grates. Smoke for 1-2 more hours.
Check on brisket after one hour. Insert a meat probe into the beef. Look for little resistance and an internal temperature of 210°F (99°C).
Remove from smoker. Leave loosely wrapped and rest for 20-30 minutes.
Slice brisket perpendicular to muscle fiber direction into thin strips. Slice each strip into small chunks. Transfer strips back to foil and allow to soak up remaining juices and marinade.
Serve into preheated tacos with your choice of filling and garnish