Slice a medium watermelon in half, then cut one half into two pieces.
Make several cuts in the watermelon; they don't have to be perfect since it will be blended.
Place the watermelon pieces into a blender. If they don't fit, use a wooden spoon to push them down.
Pulse the blender, then set the mixture aside.
Get a pitcher and place a strainer on top.
Pour the watermelon mixture into the strainer and use the same spoon to stir.
Scrape the edges of the strainer and press down until the juice starts to flow.
Discard the watermelon pulp or give it to someone with cows.
Add half a cup of sugar to the juice and mix well.
If the juice is too concentrated, add ice or water to taste.
Serve the drink in a glass, coating the rim with chamoy and Tajín, and add chamoy inside the glass.
