Thinly slice the cucumbers. Place the cucumber and onion slices in a colander and toss with the salt. Let sit in the sink or over a bowl for 30 to 40 minutes to catch the liquid that will drip out.
Rinse the cucumbers and onion in very cold water. Then, rinse the cucumbers and onion and using your hands, or better yet a clean dishtowel squeeze the liquid from the vegetables, getting as much water out as possible..
Transfer to a bowl and add the vinegar, oil, dill, sugar, and pepper. Toss to combine. Serve immediately, or refrigerate for a day, knowing the salad will soften as it marinates.