1. Wash cucumbers well; drain on paper toweling. Combine 16 cups water and salt in a very large glass or ceramic bowl; add cucumbers.
2. Cover the container with plastic wrap; let stand 12 to 18 hours.
3. Next day, pour off brine; drain well. Combine vinegar and 6 cups water in large kettle; bring to boil; add cucumbers; return to boiling.
4. Pack cucumbers tightly into 4 hot, sterilized quart jars; add 1 garlic clove, 1/2 teaspoon mustard seeds and dill sprig to each jar.
5. Bring vinegar mixture to a boil; pour into jars to within 1/4 inch of rim. Seal, as manufacturer directs; process in hot-water bath 15 minutes. Cool; label; date. Store in a cool, dry place.