In a 5-quart pot, cook bacon until lightly browned. Add onions and cook until tender (5 minutes).
Gradually add flour to onions and bacon until well-mixed.
Add enough water to the clam liquid to make 2 cups. Add to the pot, stirring constantly.
Add potatoes, salt, celery salt, and pepper. Cover and cook until potatoes are tender (10 minutes).
Chops clams. Add clam, milk, and butter. Cover and cook until heated (5 minutes). Serve.