Spiced Rum Punch with Citrus and Luxardo

Ingredients
Method
Fill 2 small freezer-safe shallow containers with 1 1/2" hot water and freeze until solid to make giant ice cubes, about 4 hours. (The bottoms of clean half-gallon milk cartons work great.)
Combine both rums, grapefruit juice, orange juice, lemon juice, liqueur, simple syrup, and bitters in a punch bowl.
Unmold ice (dip containers in warm water if needed) and add to punch along with citrus slices. Serve punch in 6-ounce glasses filled with ice.
Punch can be mixed 3 hours ahead. Chill.