In medium skillet, cook bacon over moderate heat, stirring occasionally, until crisp. Remove to paper towels, reserve 1/2 cup drippings and set aside.
Scrub potatoes and place in large saucepan. Cover with water, add 2 teaspoons salt and bring to boil. Lower heat and boil gently until tender when pierced with fork, about 25 minutes, depending on size.
Drain, peel and cut into 1/2 inch cubes. Place in large bowl; add eggs, scallions, pickles, celery seed, 1 teaspoon salt, pepper, garlic salt, mayonnaise and bacon. Toss gently until combined. At this point, mixture may be refrigerated, covered, overnight.
In small saucepan, heat reserved 1/2 cup bacon drippings, vinegar, hot water, sugar and mustard. Bring to boil, whisking constantly, and boil for 2 minutes. Pour over salad; toss gently. Serve warm or at room temperature.
If serving at room temperature, the salad may be refrigerated overnight. Bring to room temperature 1 hour before serving.
Garnish with eggs cut in to sliced or wedges, bacon, olives and parsley, if desired.