The dangers of a little information
Do not purge. Ever. You can’t possess them live and it’s a long process to do properly. Only matters in the south where they have to be alive to sell.
Immediately pull off the carapace to kill.
Twist the middle lobe of the tail left then right then pull out the guts. It’s not a “vein” it’s the crap chute. Discard. Put the tails on ice till you get home.
Rinse well with cold water, boil with potatoes corn and spices. No, you don’t get the visual effect of having a pot of whole crayfish, but the meat is delicious and has no swamp taste.
Best baits are oily fish parts - frozen minnows, trout heads and fins etc.