Too stupid to use the ET-8550 as an office printer... (Duplex printing?)

[Fried Chicken]

I've managed to make amazing pictures with the ET-8550. I've tried making my own ICC profiles, I've got the paper selected that I want, it's all perfect...
Now I'm trying to print a PDF manual I downloaded online on two pages on plain U.S. letter paper (using the mac).
My brother printer makes it very easy with a checkmark "two-sided printing".

How on earth do I do this with the ET-8550? I know it can do it b/c 1. it's advertised, 2. I've done it before... but even Epson's manual for this is useless:
https://files.support.epson.com/doc..._fy13/tasks/printing_double_mac_bus_fy14.html

I don't see the "Two-sided Printing Settings" in my print options, and I do have the Epson driver installed (not the Airprint driver).

Help?

 

[Fried Chicken]

Ok I do see an option for two-sided in the Layout section but it's grayed out:

 

[Fried Chicken]

Epson's Tech Support Number for the U.S. is:

(562) 276-1300

 

[Fried Chicken]

Speaking to epson:
The "Duplex Tumble" setting needs to unintuitively be changed to "DuplexNoTumble":

 

[Fried Chicken]

On the phone with epson I got it to print on two sides, however binding on the long edge.
Trying to change that to the short edge resulted in its printing two pages separately again.

Now I'm on hold as the indian lady speaks to higher level tech support.

 

[Fried Chicken]

The plot thickens.

Over an hour with epson support, here are the key settings that made it work:

Orientation: Portrait
2-sided Printing: On
Binding edge: 2-sided short edge
Two-Sided Printing: Short-Edge binding
Duplex Tumble: None

*notes:
1. borderless printing is not available when printing two sided
2. yes there are two "two sided printing" options, one with "2" and one with "two".

I asked the lady on the phone what on earth "Duplex Tumble" means, and she gave a generic answer "this allows two-sided printing", but when I pressed her that it doesn't make sense based on what we literally just figured out, she shut down, so it remains a mystery to me.

If attempting two sided printing, always do test prints I guess, don't just send a hundred+ page document assuming it will work.