Remove and discard the neck, giblets, and any excess fat from both ends of the duck. Prick the duck skin all over with a small sharp knife, especially along the sides under the breasts, to allow fat to escape during cooking. Fill a large pot with enough water to cover the duck and bring it to a boil. Carefully lower the duck into the water. Place a heavy lid or plate on the duck to keep it submerged (ducks float). After the water comes back to a boil, lower the heat to a simmer and cook the duck for 15 minutes. Place a long-handled spoon or closed tongs into the duck cavity, and carefully remove the duck from the water, allowing the liquid from the cavity to drain back into the pot. Place the duck on a rimmed baking sheet lined with paper towels and pat dry, inside and outside.
Prepare the grill for indirect cooking over high heat (230° to 290°C).
Season the duck with the salt and pepper inside and outside. Bend back the wings and tie the legs together with butcher’s twine. Brush the cooking grates clean. Grill the duck over indirect high heat, with the lid closed, for 30 minutes. Brush the duck all over with 2 tablespoons of the hoisin sauce, and continue grilling until the skin is dark brown, about 10 minutes more (turn if necessary to prevent the sauce from burning on the bottom). Remove from the grill and let rest for 10 to 15 minutes before carving. Serve warm with the remaining hoisin sauce.