Different from a wetback. Drenchedbacks are people immigrating from the southern boarder (excluding mexicans) to the U.S. They are called this instead of wetbacks because they have to travel farther and swim more then the mexicans, thus getting more wet.
"That Mexican that just crossed the boarder is a wetback"
"That guy from El Salvador is not a Mexican so he can't be a wetback either......therefore, he is a drenchedback"