duplex (double sided) print not available

Just worked this out! Ignore the "duplex" section of the print dialogue. Instead:

Print dialogue > Device > Two-sided > Long-Edged Binding > OK

Using Evince, for example:

1. Select File > Print.
2. Click the Page Setup tab.
3. Set Two-sided to: Long Edge (Standard)
4. Click Print.

I have a similar problem with an EPSON XP-415 printer which, in Windows, can print two-sided, although only with manual intervention half-way to put back the one-sided printed paper in the loader.

The method to print two-sided:

1. Print only odd pages
2. Flip and load back in the paper rack the group of pages printed
3. Print only even pages