Fill an 80-quart crawfish boiling pot with a basket 1/3 to 1/2 with water. Add onions, garlic and lemon halves.
Bring to full rolling boil. Stir in Crab Boil Complete. Add potatoes. Reduce heat to medium-low. Boil 20 minutes or until potatoes are fork-tender. Remove potatoes.
Return water to full rolling boil on high heat. Add crawfish and other seafood meats, celery, liquid Crab Boil and Crab Boil bag. Return water to full rolling boil on high heat.
Start checking doneness just before water returns to full rolling boil. As soon as small gaps start to appear between the head and the tail on the largest crawfish, they are done.
Turn off heat. Add frozen corn and cooked potatoes. Let stand 15 minutes. Remove corn and potatoes. Let crawfish and other meats stand for a minimum of 30 minutes, but 45 minutes is better.