Wash and scrub the cucumber well, then slice thinly, ideally using a mandolin. Put the cucumber slices in a medium bowl and add 3 ounces vinegar, and the water, salt, and sugar, stirring as you go. Let it sit for 4-5 minutes, then drain off 2 ounces of the liquid—cucumbers release a lot of moisture. Add one additional ounce of vinegar, to taste, and stir again. Taste and adjust seasonings as needed.