I have just now filled our DEF tank for the second time (16 gallon tank). Our chassis manufacturer moved the filler to the driver's side on the 2015 model (maybe the 2014 model too). Anyway, the clerk had to explain to me the process of working the pump with DEF. Unfortunately, the girl told me wrong so the DEF wouldn't activate.
Since the DEF tank wasn't totally empty the first time I waited until I needed diesel again. The process to fill, is to fill with diesel first, put the handle back in the holder, then hit the big blue DEF button to start that pump.
The DEF handle is behind a separate door that you slide up so that there is no confusion to accidentally pick the wrong handle. Since I can go about 2,300-2,400 miles on my DEF tank, it's not a big deal.
I paid $2.88 a gallon for DEF, $2.91 for Diesel at the T/A truck stop in Wilcox, AZ.
MM.