In a large heatproof measuring cup, combine the vinegar, sugar, salt, mustard seeds, coriander seeds and dill seeds with the hot water and stir until the sugar and salt are dissolved.Let the brine cool.
In a large bowl or mason jar, toss the cucumbers with the dill and garlic.Pour the brine over the cucumbers and turn to coat.Place a small plate over the cucumbers (if using a large bowl) to fully submerge or fully fill the mason jar with the brine.If using the bowl, cover the bowl with plastic wrap.
Refrigerate the pickles overnight, stirring once or twice if you like.
Serve cold.The dill starts to fade and lose its vibrant green color after awhile.
