Thanks. It was incredibly confusing. The option for two-sided printing should be on the print settings, but it's not. After around 20 minutes of digging I found it. Works perfectly now.I have a WorkForce 845, which I assume is somewhat similar.
The two-sided printing has worked fine with my iMac for over 2 years now. However, the Epson menus on the Mac are indeed confusing and it can take awhile to get the printer working the way you desire. I don't claim to understand it all.
Make sure you have the latest version of the Epson print utility. Then start trying the different options. One confusing thing is that the duplexing seems to be accessible from at least two different setting menus. I recall having to play with both of them before getting it to work. I have no experience with the printer on Windows so can't compare.