Prep: 10 minutes; Chill: 1 hour
1. Puree watermelon, in batches, in a blender or food processor. Pour puree through a wire-mesh strainer, pressing with the back of a spoon; discard pulp and seeds.
2. Combine watermelon liquid, tequila, and next 4 ingredients in a large pitcher. Cover and chill 1 hour (longer for a stronger pepper flavor). Serve over ice. Garnish, if desired.