Chop the onion. Peel and dice the potatoes to uniform size, about 1/2 inch cubes. In a large stock pot, melt the butter over medium-high heat and add salt pork or bacon. Add the chopped onion, and sauté until the onion is translucent. Add the water, clam juice, bay leaf, and potatoes. Simmer until the potatoes are tender.
Chop the clams, then add the clams, crab, lobster meat, and shrimp to the pot. In a separate small pot, scald the milk but do not bring to a boil. Then add the scalded milk to the large stock pot. Stir minimally, then add the scallops and place the haddock on the top. Let simmer for 1 hour, stirring minimally, and do not let boil. (You may need to add more milk or half and half due to large amounts of seafood.)
Serve the chowdah with oyster crackers.