Start a pot of water with some onions, whole mushrooms,corn on cobb, whole garlic cloves, new potatoes, smoked sausage pieces, a couple of split lemons, package of crab boil,1 container of Tony Chacheres seasoning, 1 bottle of hot sauce,1 bottle of tabasco, and half a cup of kosher salt.
Put the crawfish in a container with tap water. The chlorine will make them puke and crap out all the stuff in their belly.
Throw them in the pot, wait for it to boil - they should start to sink - Once at a boil, remove from heat and ice immediately. Just to stop the cooking process. Then strain off the brine and pour the bugs/veggie mix onto a table covered in newspaper.
Get good beer and enjoy.
On the tail - the center scale - twist and pull - the vein usually slides right out if that bugs you. I eat it all. Pull the tail off and suck the juice from the head!