Mai Tai

1 measure/1 1/2 tbsp light rum
1 measure/1 1/2 tbsp dark rum
1 measure/1 1/2 tbsp apricot brandy
3 measures/4 1/2 tbsp orange juice
3 measures/4 1/2 tbsp pineapple juice
1 measure/1 1/2 tbsp grenadine