German

I recently saw an authentic Gas Mask in an Army / Navy store, and I was puzzled to see a German saying "Hier Stopfen Abziehen Dann Kappe Abschrauben." I was wondering what the rough translation of this German phrase was, and why it is on a gas mask.

"Then place plug here when unscrewing the cap."

There's a fun place to go for simple translations to and from English and a few European languages:
babelfish.altavista.com/ cgi-bin/translate?