Epson CX6500 Reference Manual page 160

Depending on the media type, stacks of up to 30 sheets can be loaded into the sheet feeder
during double-sided printing.
Only use media types that are suitable for double-sided printing. Otherwise, the printout
quality may deteriorate.
Depending on the media type and the amount of ink used to print text and images, ink may
bleed through to the other side of the paper.
The surface of the paper may be smeared during double-sided printing.
Standard double-sided printing for Windows
Follow the steps below to print odd- and even-numbered pages onto opposite sides of the sheet.
Access the printer
driver.
Accessing the Printer Software for
Windows
Click the Main tab, then select a Quality Option setting. For details, see online
help.
Select a paper Type
setting.
Media Type
Settings
Select a paper Size
setting.