Combine the cucumbers and salt in a large, shallow bowl; cover and chill 1½ hours. Move the cucumbers into a colander and rinse thoroughly under cold water. Drain well, and return the cucumbers to bowl. Add the onion to the bowl.
Combine the sugar and the remaining ingredients in a medium saucepan; bring to a simmer over medium heat, stirring until sugar dissolves. Pour the hot vinegar mixture over the cucumber mixture; let stand at room temperature 1 hour. Cover and refrigerate 24 hours. Store in an airtight container in refrigerator up to 2 weeks.
Notes
Don't cut the cucumbers too terribly thin. You want them to have a little bit of crunch to them!
You may find that your cucumbers are already ready to sample within just a few hours of marinating in the pickling liquid (rather than waiting an entire 24 hours!)