How to use the duplex function for HP4300

["Li Daobing" <lidaobing@gmail.com>]

Hello,
  my printer is HP4300 with duplex function. I use Debian system and
cupsys to manage the printer, but I don't know how to make the duplex
function work. I select 'Duplex Installed' on page [1], and when I use
evince to print a pdf document, I also check [2], but the duplex
function still not work.
  What should I do?
  cupsys version: 1.1.23-11

[1] http://127.0.0.1:631/admin/?op=config-printer&printer_name=hp4300
[2] File->Print->Printer->Configure->Duplex