In a mixing glass, squeeze and add a slice of orange, white sugar and several mint leaves over a couple of ice cubes or a bit of crushed ice.  Lightly muddle until the sugar dissolves and you smell the mint.  Fill the glass half way with ice, add orange flavored rum and shake. Strain over cracked ice in a highball glass or double rocks glass. Top with soda water (or 7-up if you want a sweeter drink), garnish with mint sprig and orange slice and serve.