Combine the black pepper, kosher salt, and garlic powder.
Trim the fat cap to ¼-inch to ½-inch thick, then rub the brisket all over with the spice rub. Let the brisket sit at room temperature for 1 hour.
Start the smoker and get the temperature up around 225 to 250°F. Fill a disposable aluminum pan with water and set it on the smoker to create humidity. You will want the water pan to be full during the smoke.
Place the brisket on the smoker fat side up and close the lid. Leave the lid closed and smoke the brisket for at least 3 hours, then start to check it every 30 minutes or so too see that a nice dark color is developing, spritzing the surface of the brisket with water or vinegar in a spray bottle if it starts looking dry.
When the brisket has a dark color and reaches an internal temperature of around 165°F to 170°F on an instant read meat thermometer (around the 5 to 6 hour mark), you might choose to wrap your brisket in unfinished butcher paper, peach paper, or foil. There's nothing scientific about this, just wrap it all up by folding the paper or foil around the meat and stick it back on the smoker.
Continue to cook through the stall (a long period where the temperature of the brisket doesn't go up and may even decrease a bit). This can go on for hours, but don't worry, it's totally part of the process of making truly amazing smoked brisket.
The brisket will be done when the internal temperature reads somewhere between 200°F and 210°F when measured in the middle of the flat part of the brisket (203°F seems to be the magic number). You can also tell doneness by feeling the brisket with a thin, clean towel to see if it is soft and tender.
Remove the brisket from the smoker and let it rest for 1 to 2 hours, still wrapped, until the internal temperature drops to 140°F to 145°F, then slice against the grain and serve.