The only thing that makes a crawfish purge themselve is Time without food. Salt only makes them puke, and running water over them only rinses the outside. True purged crawfish are left in huge vats without food for a prescribed period of time. Hawks Restaurant between Rayne and Crowley has the only purged crawfish I know of and they purge onsite. What would be the difference in pond crawfish and deep water crawfish as far as having to purge? Always rubs my azz when I see my wifey and inlaws picking the vein out of a boiled crawfish!
Eat the whole tale damnit! and stop wasting dat meat.