Cut off ½ inch from the bottom end of the watermelon so that it sits on a flat surface. Make sure that the surface that the watermelon will sit on isn’t cut too deep, just enough for it to sit evenly. Cut about 2 inches from top to end, cutting through the rind completely in order to get at the flesh.
Using a large spoon, scoop out watermelon flesh from the top of the watermelon and transfer it to a bowl, making sure to leave about 3 inches of flesh at the bottom of the watermelon for the spigot to nestle into.
Determine where to place the spigot in the surface of the watermelon, then press it firmly into the rind to make an indentation. Using a pointed paring knife, create a small opening, making sure to cut inside the line of the circular indentation.
Press the spigot gently into the hole. Scrape away the flesh on the inside of the watermelon to reveal the end of the spigot.
In a blender, combine 4 to 6 cups watermelon flesh with 4 to 6 cups water or alcohol. Fill watermelon with liquid and serve over ice.
Makes 8 to 12 cups, depending on the size of the watermelon.