I know I'm late in answering this question but I just bought the DeskJet 3512-e All In One Series and had to figure this one out as well. For this printing I printed a pdf file in Adobe Reader.
To print both sides of a page I had to go to the top left of the page I wanted to print and click on File. Scroll down to the Print icon, click on it and go to "More options" box. Its 1/3 the way down the page, click it.
There is a box that says "All pages in range", click it. Choose "Odd pages only", this will print pages 1,3,5.7,9, and so on. When finished printing odd numbered pages, take the stack of pages that you just printed and put it in the paper input slot.
The printed side should face away from you. The blank side will face you. Make sure that you put the top of the page faceing down in the paper input.
Now go back to the same print document page. Go to File again, scroll down to print. Then go to "More Options" again, but this time click on "Even pages only".
Now this is were I messed up.
If there is an odd number of pages, you should remove the last odd numbered page before you put the stack of papers back in the printer input as described above..
The printer will start printing even numbered pages on the first page available. In my case it printed page 92 on the back of 93. The last page, 93 should have had nothing on the back.
This left the last page at the end of the printing cycle, page 1, sitting in the paper input slot with nothing printed on the back of it.
Since this was not a report to be handed in to school or work I didn't have to reprint everything.
I hope this helps save some paper.
Bill McDonald