Fill two large stock pots with 5 gallons water, each (leaving room for many other ingredients). Mix half the salt, Old Bay, lemons, cayenne pepper, garlic, onions, celery, bell peppers, and oil into one pot of water and half of each into the other pot. Bring the mixtures to a boil. Reduce the heat and allow to simmer for 10 minutes.
Add half the sausage, potatoes, and corn to one pot and half to the other, and simmer for 15 minutes. Add half crawfish to one pot, and half to the other. Simmer for 12 minutes. Turn off the heat.
Use a large colander to strain everything from the liquid in both pots. Pour remaining crawfish and vegetables onto a large serving tray covered with newspaper. Serve immediately.