Place dill, garlic, red pepper flakes, and onion in a large mason jar. Fill jar to top with cucumbers.
Meanwhile, place the water, vinegar, sugar, salt, and pepper in small saucepan over high heat. Whisk until the mixture comes to a boil. Pour hot liquid over cucumbers. Cool slightly, then place top on jar and refrigerate overnight.
SNAPPY TIPS: We had better luck with small cucumbers rather than larger ones. Make sure your cucumbers are completely covered with the liquid. Depending on your jar and size of cucumbers, the recipe may take a little more or less than 3 cups of cucumbers. For a less spicy pickle, reduce the red pepper flakes.SNAPPY SUBSTITUTIONS: Instead of sugar, you could use honey. Instead of a large mason jar, you could use another large container although I would suggest not using plastic.