Wash the cucumbers in cold water. In a large pot, make a brine from the vinegar, 3 cups of water, and salt and bring to a boil. In the bottom of a sterilized quart jar, place a generous layer of dill (seed heads, leaves, and stems are all suitable), ½ to 1 clove of garlic, and ½ tablespoon mustard seed. Pack the cucumbers vertically into the jar until it is about half full, then add more dill and fill the remainder of the jar with cucumbers. Repeat, using all of the cucumbers and jars. Fill the jars to within ½-inch of the top with the boiling brine. Seal and process in a boiling-water bath for 15 minutes; start counting the processing time when the water starts to boil. Note: Pickles may shrivel after the processing but will later plump in the sealed jars.