Add the corned beef to a large plastic container and cover with cool water. Store in the fridge for 24 hours, changing the water out about halfway through.
Once the corned beef has soaked for 24 hours, remove it from the water and pat dry.
Combine the black pepper, brown sugar, garlic powder, onion powder and paprika in a mixing bowl and stir until well combined.
Season the corned beef generously with the dry rub mixture, being sure to coat every side.
Allow the beef to rest at room temperature while you preheat your smoker to 250°F.
Once the smoker is preheated, add your beef directly to the grates and let it smoke for about 4 hours until it reaches 165°F.
Wrap the beef tightly in butcher paper, then place it back on the smoker until the internal temperature reaches between 195°F and 205°F (about 2 more hours).
Remove from the smoker and let it rest at room temperature for 1 hour, then slice and enjoy!