Slice the top sixth of your watermelon lengthwise using a sharp knife. (Don’t worry if it’s not exactly a sixth. Just cut a “lid” off that exposes enough of the melon to hollow it out easily, okay?) Please do this sober.
Scoop out the flesh of the watermelon until the rind is left with minimal pink showing.
In a blender or food processor, puree the watermelon in batches. Strain the puree through a fine mesh strainer, and discard the solids. You should be left with about 9 cups of watermelon juice.
Pour the watermelon juice back into the watermelon punch bowl. Add the vodka, lime juice and club soda and stir to combine.