In a pot on the stove, combine the vinegar, sugar, salt, mustard seeds, and coriander seeds with the hot water and bring to a boil. Stir until the sugar and salt are dissolved then remove from heat.
1 ½ cups distilled white vinegar, ¼ cup sugar, 4 teaspoons kosher salt, 1 teaspoon mustard seeds, 1 teaspoon coriander seeds, 2 cups water
In a large heatproof container, toss the cucumbers with the dill, sliced onions, and garlic.
2 pounds kirby (pickling) cucumbers, 1 large onion, ¾ cup fresh dill, 4 - 6 garlic cloves
Pour the brine over the cucumbers and mix to get the brine fully distributed.
Place a small plate or upside-down jar over the cucumbers to keep them submerged, then let the pickles and bring cool to room temperature.
Once cooled, transfer to an airtight container or jar. Refrigerate the pickles and serve cold.