1. Fill a large pot halfway with water and bring to a rolling boil. While water is heating, transfer crawfish to a large cooler or wash tub. Run water over crawfish with a hose until water runs clear and mud is gone. (Be sure to skim out any dead crawfish, sticks, and anything else floating in the water that you don’t want in your boil!) Transfer crawfish into a clean cooler.
2. To the boiling water, add salt, boil seasoning, liquid boil, and thyme; stir until salt and seasoning blend dissolve. Add straining basket and fill with onions, garlic, and celery. Cook in boiling water for 5 minutes. Add potatoes and cook for 5 minutes. Add corn and cook 5 minutes more.
3. Remove basket and add clean crawfish, mushrooms, and andouille; carefully lower back into pot. Bring water back to a rolling boil and cook for 5 minutes. After 5 minutes, immediately turn off heat and stir in ice to lower the heat. (The goal is to get the mixture to between 170 and 180 degrees to let the crawfish soak in all the flavors without overcooking.) Add hot sauce. Squeeze lemon juice over crawfish, then add squeezed lemon halves. The longer the crawfish soak, the more flavor—and spiciness—they absorb. Try around 30 minutes for regular crawfish and 45 minutes if you like them spicier.
4. Remove crawfish and immediately transfer to a cooler. Sprinkle Cajun seasoning in layers over crawfish and close cooler. Let steam for 10 minutes before serving.