1. Place the watermelon cubes in the gin and place in the fridge. Soak for 4-6 days.
2. Strain the watermelon and place the gin back in your bottle.
3. In a large glass filled with ice, add equal parts of watermelon-infused gin (1oz is typical for one cocktail), Campari and sweet Vermouth. You can also add a splash of fresh lime juice (.5oz is plenty).
4.  Stir with a spoon or stirring stick for about 30 seconds, then strain into a cocktail glass, with one large ice cube.

Garnish with a wedge of watermelon.