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?
Simply put, crawfish are fresh water. If you put them in salt water they cannot breath and they die. All they need is to be rinsed well where they don't muddy the water they are boiled in since that is what you are ingesting when You blow the heads.
Crabs on the other hand can handle salted water, although the high salininty will cause them to purge themsleves. Also, they are usually not that muddy and you are not sucking in the water they cooked in.