Print From Your Computer : Macintosh Printing (OS X 10.3 and 10.4)

Print Double-Sided With the Optional Auto Duplexer
If you have the optional auto duplexer, you can print on both sides of the page automatically.
1.
Select Auto Duplex Printing Settings from the pop-up menu.
2.
Select Auto Duplex Printing.
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When you’re finished, you’re ready to print.