Add the potatoes to a large pot of cold salted water, and bring to a boil. Cook just until tender (about 10 minutes). Drain the potatoes, and then transfer them to a large bowl. Drizzle pickle juice over the warm potatoes and toss gently. Let them cool to room temperature.
In a medium bowl, whisk together the mayonnaise, buttermilk, mustard, sugar and pepper. Pour this mixture over the cooled potatoes. Add the eggs, onion, celery and pickles, and toss gently to blend. Season to taste with salt. Cover and refrigerate (can be made up to 8 hours ahead).