Poach the duck first in salted water. To do this, put the duck on the chopping board and remove the fat deposits in the cavity. Cut the neck off and remove the first two wing joints. Fill a pot large enough to cover the duck with water and bring to the boil. When the water is boiling, add the sea salt, and then add the duck, breast-side-down. Keep the water simmering and cook for 25 minutes, then turn the duck over and cook for a further 5 minutes. Remove the pot from the heat and allow the duck to cool in the poaching liquid. When cool, remove and pat dry with paper towel. Cut the duck into two legs and two breasts and proceed with the barbecuing. Make sure you place the duck skin-side-down first on the grill, and watch out as the fire flares up when the duck fat drips down.