Freeze 5 cups seedless watermelon pieces to measure 5 cups in a sealable plastic bag. Freeze for 3 hours to 1 week. Mix the frozen watermelon with 1 cup of Sauza Hornitos Tequila, 1/2 cup fresh lime juice and 1/4 cup sugar in a 6 cup blender container. process til thick and smooth. Pour into 5 or 6 glasses to serve.