No one mentions that DD was based on a comic strip that ran in the National Lampoon in the '70s. I'm surprised it's become so "obscure"...
I believe the mag was Cheap, not National Lampoon.
Dirty Duck the movie is unrelated to Dirty Duck the comic strip. Basically what happened was the guys working on the movie decided to plagiarize the name (as well as the general premise of a sex obsessed duck) to encourage wider distribution of their film because the comic strip was popular at the time. It would be like if someone decided to make a cartoon about a stage magician named Harry Potter today.
The Dirty Duck comic strip still runs in Playboy today.
Actually I just looked at the Dirty-Duck-the-Comic-Strip website and it would be like Bobby London plagiarizing the drawing style of George Herriman's Krazy Kat, which was popular with the cognoscenti in 1970, to do an off-color, countercultural cartoon. Thanks for clarifying the relationship between the movie and the strip, though.