Question for you master boilers - boil crawfish or crabs first?

bayoubadboy said
Btw, unlike crawfish, you can purge crabs in salted water. This is recommended so that the crabs "throw up" .

Just out of curosity, I've got friends who purge crawfish in salt water and some who purge in fresh water. Both swear their way is right. What is your opinion on purging with saltwater, or rather, why you can't?

Thanks