Watermelonade

[from epicurious]

1 (12-lb) watermelon (preferably seedless)
1/4 cup sugar, divided
4 tsp fresh lemon juice, divided
16 cups ice cubes, divided

garnish with lemon slices & mint sprigs.

Cut watermelon flesh into 2-inch chunks and discard rind. Purée one fourth of watermelon in a blender with 1 Tbsp sugar, 1 tsp lemon juice, 4 cups ice, and a pinch of salt. Strain through a fine-mesh sieve into a large bowl, discarding solids. Make 3 more batches. Add sugar to taste if desired and serve over ice. You can also make this one day ahead and leave in the fridge to chill. The drink will separate, so you'll have to stir it up a bit before serving.