Just got done with my company's fifth annual Crawfish Boil.
Imagine, if you will. A 15 or 20 gallon pot. A steel cage to drop in it. Red potatoes. Whole white onions. Mushrooms. Two different kinds of sausages. Corn on the cob. Enough Cajun seasoning to sterilize the innards of an army.
And a a couple thousand Crawfish. I think we had 2400 or so.
First, you fill the pots about 3/4 or so with water, and get them going on propane burners.
Once it's hot, you pour in the Cajun seasoning and get it to a rolling boil.
Meanwhile, the live Crawfish are on ice to keep them alive...ish. You dump them out into a container like a beer cooler and put a hose to them until your container is full to the top. The dead ones should start floating, and you wanna take those out ASAP before their toxins cause other Crawfish to die.
Once they're clean and drained and sort of picked through (because understandably, they will pincer the shit out of you if you aren't careful), you load them into the steel basket, and add all your fixins on top of them. Let boil for 15 to 20 minutes, stirring (if such a thing can be called a stir) occasionally to shift the bottom contents of the pot to the top (carefully, or you will be a in world of hurt.)
When you've got a nice rolling boil visible at the top, and it's been about 20 minutes, you kill the heat and let it continue to steam cook for about 10 minutes.
Then, you remove the cage and manhandle it to a beer cooler with the help of another person, and shake the basket side to side, letting portions fall out. As each big portion falls into the beer cooler, a third person with a can of yet MOAR Cajun seasoning liberally shakes it out, coating the whole mass in dry seasoning.
Close the lid to the beer cooler and it steep for 10 to 15 minutes. You know, so the spice really gets in there and goes from hot to mouth-annihilation.
After its steeped, pick up the ice chest and dump the contents onto a table you preferably built out of plywood, covered in plastic, with circular holes cut on each end, with trash cans under them that also serve as the legs.
And then you eat. I recommend having a lot to drink on hand, like epic quantities of shitty beer.