Single drink, frozen: Add the grenadine to the bottom of a highball or hurricane glass. Blend the dark rum, coconut rum, lime juice, pineapple juice, and ice in a blender until a slushy texture forms. Pour the blended mix slowly over the grenadine. Garnish with pineapple or lime wedges.
Single drink, on the rocks: Add ice to a glass (you can also use crushed ice). Pour in the dark rum, coconut rum, lime juice, and pineapple juice, and stir gently. Pour the grenadine into center of the drink and it will sink to the bottom.
Pitcher variation (4 drinks): Blend ½ cup dark rum, ½ cup coconut rum, ¼ cup lime juice, 1 ½ cups pineapple juice and 4 cups ice in a blender until a slushy texture forms. Place 1 tablespoon grenadine in each cup, and pour in the blended mixture.
Notes
*To convert to tablespoons, 1 ounce = 2 tablespoons