A recipe for cooking a whole duck in a crock part starts by preparing the duck. Remove the giblets and trim any fat. Place the duck on a large piece of cheesecloth, which enables it to be easily lifted from the crock pot when it is finished.
To finish preparing the bird, pat dry with a paper towel and sprinkle inside and out with salt and pepper. Put a quartered onion and an aromatic, such as an apple, orange or lemon, into the cavity, along with two springs of Rosemary and a bunch of Thyme. At this juncture, it is optional sear the bird over medium-high heat on the stove to brown it. It does not affect the flavor, but makes the duck appear roasted.
Using the cheesecloth, place the bird into the crock pot. It should not be placed directly onto the bottom of the pot, so use either a wire rack, balls of aluminum foil or vegetables, such as carrots and potatoes, to keep it off the bottom. Pierce the skin of the duck several times and cover with the cheesecloth. Cook on low for six to seven hours, or high for three to four hours. The duck is done when the internal temperature reaches 185 degrees Fahrenheit.