Start by gathering and prepping all ingredients. In a large stockpot, bring 6 quarts of water to a rolling boil. Stir in ¼ cup of seafood seasoning, allowing the fragrant blend to infuse the water.
Add the red potatoes to the seasoned water and boil for 15 minutes, giving them a head start to cook through.
While the potatoes are cooking, fill another large pot with water and bring it to a boil. Add 1 teaspoon of seafood seasoning, then carefully lower in the crab legs. Simmer for approximately 10 minutes, or until the crab meat is hot and tender. Drain and set aside.
To the pot with potatoes, add the chopped carrots, celery, and pearl onions. Continue boiling for another 10 minutes until the vegetables are fork-tender.
Next, stir in the sliced sausage and husked corn. Let the mixture boil for 5 additional minutes, allowing the flavors to meld and the corn to brighten.
Finally, add the shrimp and pre-cooked crab legs to the pot. Cook for 2 to 3 minutes, just until the shrimp turn pink and opaque.
Serve the seafood boil hot, preferably poured onto a newspaper-lined table or large platter for a communal, hands-on experience. Sprinkle with extra seafood seasoning if desired.