Place the watermelon in a bowl to stabilize while pureeing. Carefully cut a hole at the top of the watermelon big enough to fit the tip of an immersion blender. Blend the inside of the watermelon so that all the pulp has turned to liquid.
Carefully strain the juice through a fine mesh strainer and reserve in a large container. Using an apple corer, punch a hole into the side of the watermelon big enough for a nozzle to fit. Securely attach the nozzle to the watermelon and fill with reserved watermelon juice. Add the tequila and the limeade and stir.
Fill 8 glasses with ice and serve the margaritas with a watermelon wedge for garnish.