Drain clams, reserving liquor. Fry pork to golden brown, then add onion and fry to light golden. Add a layer of potatoes and sprinkle with flour, salt, and pepper. Add clams, then another layer of potatoes, sprinkled with the remainder of the flour and with salt and pepper. Add boiling water and simmer until potatoes are done (18 to 20 minutes). Combine milk, clam liquor, and butter; add to the clam mixture. Simmer 5 minutes. Serve with crackers.