Brush outside of buns with butter; sprinkle with poppy seeds.
Bake buns, split sides down, at 350 degrees until warm, about 5 minutes.
Simmer hot dogs in water for approximately 10 minutes; transfer to buns.
Squirt yellow mustard over each hot dog; top with sweet relish.
Divide onion among hot dogs.
Arrange a dill pickle spear on 1 side of each hot dog and 2 tomato wedges/slices on the other side.
Top each with 2 sport peppers or a pepperoncini.
Sprinkle with celery salt and extra poppy seeds.