How to print on custom paper sizes with Epson WF-7510 printer?

I am an architect and haven't printed on 12 x 18 paper lately. I was having a hard time getting my Epson WF-7510 printer to print an entire image -- it would only print a partial 8.5 x 11 image on the 12 x 18 paper. I found the solution in a post from about 4 years ago, so thought I'd bump this subject in case anyone has similar issues.

To solve my problem, I went to System Preferences>Printers, and deleted the printer. I then added it back, ensuring the the WF-7510 driver was selected and not AirPrint. It now works correctly. (I am still using MacOS Sierra.)