Preheat an oven to 500 degrees F and arrange the oven rack in the center of the oven.
Remove the innards of the duck and reserve them for another use, or discard. Remove any loose pockets of fat surrounding the cavity. Season the inside of the duck with salt.
In a pot large enough to hold the duck, combine the water, 3/4 cup of the soy sauce and 1/3 cup of honey. Bring the mixture to a simmer over low heat. Add in the brine from the green peppercorns, lower the heat and submerge the duck, breast side down, into the pot. Let it simmer 30 seconds, basting the top side with the liquid. Remove the duck and arrange it, breast side down, in a roasting pan fitted with a rack that elevates it off the bottom of the pan. The rack will allow hot air to circulate around it as it cooks. (Cook's note: Ideally, the duck should sit overnight to allow the flavors to meld with the meat and for the skin to dry out. This will mean a crispier skin, once the duck is cooked.)
Put the roasting pan into the oven and turn the temperature down to 400 degrees F. Allow about 15 minutes roasting time for each pound of duck. Cook for 20 to 25 minutes, remove the pan from the oven, then flip the duck. Using a turkey baster, remove the excess fat from the bottom of the roasting pan and transfer it to a heatproof liquid measuring cup. Return the duck to the oven and cook for another 45 minutes to1 hour, depending upon the size of your duck.
Meanwhile, in a medium pot, combine the champagne vinegar with the remaining 1/4 cup soy sauce, 1/4 cup honey, Marsala and the reserved green peppercorns. Bring the ingredients to a boil over high heat. Lower the heat and simmer gently, allowing the glaze to reduce and the flavors to blend. Taste for seasoning. Allow it to cook until all the flavors meld together.
Remove the duck from the oven and baste it with the drippings in the bottom of the pan. The duck should register about 150 F when an instant-read thermometer is inserted into the thigh meat. Transfer it to a platter and pour half of the glaze over the breast and thigh meat. Reserve the remaining glaze for plating. Allow the bird to "rest" for about 15 minutes. Carve the duck and arrange on a serving platter. Season the flesh, with salt, if desired, and top with remaining glaze.
Reserve any fat that accumulated at the bottom of the pan. I use that duck fat like oil or butter for cooking. It's delicious!