Combine pickle brine, water, sugar, and black pepper in a (32-oz.) jar. Seal jar and shake until sugar is dissolved, about 1 minute.
Pack cucumber, tomatoes, onion, celery, dill, and parsley into jar. Seal jar and shake until brine evenly coats vegetables.
Chill in refrigerator for at least 1 hour or up to 24 hours, flipping the jar occasionally to ensure vegetables marinate evenly.
Transfer salad to a bowl and serve with a slotted spoon or tongs. Serve chilled.
