Set a colander over a large bowl; place the cucumbers, onion, and salt inside the colander and gently toss. Let sit for 30 minutes, allowing liquid to drain.
Rinse and pat dry.
In a large bowl, whisk together the mayonnaise, sour cream, dill, vinegar, sugar, and a sprinkle of salt and pepper.
Add in the cucumber and onion; toss gently to combine, ensuring the cucumber and onions are well coated.
Serve right away.
