If you want a two-sided print-job, draft quality:
This is the default. Go to Print > Properties... you'll see "FastRes 1200" under the "Paper/Quality" tab's Print Quality box, and over under the Printing Shortcuts tab, "two-sided (Duplex) printing" will be selected.
If you want a two-sided print-job, formal quality:
Same, but you'll want to pick "ProRes 1200 (170lpi)."
When you're going back and forth, check to make sure your number of copies and collation settings in the original print dialogue of the application you're printing from haven't changed. Some programs, including Microsoft Word, may reset to their defaults after you've changed the printer properties.
If you want a single-sided print job:
This is where things get unnecessarily tricky. You have to go to the "Paper/Quality" tab first, then select "General Everyday Printing." New settings appear on the right, and the default paper setting is, bizarrely, A4. Change that to "letter." Now go back to "Paper/Quality" and pick your resolution, FastRes or ProRes, depending on whether you want draft quality or formal quality. And, before you go, select "Tray 2" from "Paper Source." "Auto Select" doesn't work.
If you leave it in auto select, the printer will halt when it's time to do your print job. You can still get your print job, you'll just have to go up to the printer and hit the green check button twice - once to "print from another tray" and the second time to "print from Tray 2." It's really a joke, and sometimes print jobs get ridiculously backed up.
Yesterday I had to frig around with the printer to get someone else's job to print, then that and a bunch of other jobs came out, then it stalled again with mine. And then I realized that the "auto select" wasn't working when people wanted non-duplex printing. Seated back down, I laughed to myself when the clueless ITSS assistant was like, "Uh... the printer's working again." She was a lot of authoritarian bluster and not much skill - earlier she'd said, "Just a reminder, when the labs are full like this, they're restricted to academic work only. No e-mail, no Facebook*..." That's gotta be a joke - the labs are always "full like this," unless you're here at three in the morning.
* - This rubbed me the wrong way, because at the moment I was using Facebook messages to communicate with a friend about a possible job opportunity. It's not academic work, but since part of the point of my being here is to make myself more employable, I believe this sort of use is acceptable at any time.
Anyway, hope this helps. Just remember to select "General Everyday Printing," "letter" and "Tray 2" in printer properties when you want single-sided printing, and you should be A-OK.