I'm using an iMac with a G4210 printer. I cannot figure out how to duplex or print double sided. In the printer dialog box there isn't an "Duplex" box available to check, only a "Black and White" box. And lower under "Layout" there is a "Two-sided" option, but it's grayed out. My ancient Pixma even printed duplex with this iMac. Any suggestions/recommendations? Thanks!