Use at least a 20 oz glass. Measurements are estimated, adjust size of glass for stronger drink. Put ice in glass and pour in rum. Add roughly equal parts 7-up and Orange Juice. Put in a splash of grenadine for color. Stick cocktail umbrella in a slice of orange and place on top of drink (this is only for presentation and not needed for serious drinking). As with any great drink, adjust portions to taste. Repeat several times until you feel like you're on a deserted island.