Duplex printing - use mpage

My favourite option:

mpage -t -2 -Pprintername your.ps
hendry@bogrund-14:~$ mpage -t -Pps8 agiledev.ps
hendry@bogrund-14:~$ lpq -Pps8
net-ps8 is ready and printing
Rank   Owner      Job  Files                                 Total Size
active hendry     80   (standard input)                      1097686 bytes