Add all ingredients except for black rum to a glass and stir to combine. Fill a Collins or other tall glass with crushed ice. Add the mixed drink to the glass with ice. Top with the float of black rum.

*To make rich simple syrup, combine two parts sugar and one part water in a pot. Set heat to medium-low and stir until sugar dissolves. Chill before using.

Garnish as desired and serve with a straw.