Happened to be next to a Pilot and noticed their DEF pump lines were empty. Just at 10K and I filled it again. It took 4.6 gallons. The only other time I filled it was around 5K and it took 4.4 gallons.. My math says 9 gallons for 10K miles with about 2K of that towing. So...I now know I can figure about 1,100 mpg on the DEF.
There's more. Second time I used a bulk pump. First time there were no issues. This time I pulled the handle on and got a DEF shower. Ended up holding the handle in just a bit to find a flow rate that did not kick back. Did that until it clicked off. Tried to fill more and each time it clicked off. There IS a flapper in the filler to help retard the kick-back. Did not help much for me. I got wet and so did the truck.
Now, if you do not have a filler cap on your fuel filler that means you WILL get DEF splashed into your fuel filler. Not good. Not good at all. Especially since you will not be able to get it out.
I'm ugly, not stupid.. I have a filler cap.
That DEF on my hands turned the skin a bit white or it left a white deposit on the skin when it dried. I near immediately closed both caps up and poured water from the washer sponge on the windshield scraper. Scraped the stuff with that water.
After returning home I washed and waxed where the DEF spilled. No damage I can see. Hand still feels a bit "tingley". Washed the heck out of it a couple times so far. No skin stain evident now.
In summary, 1,100 mpg DEF. Slowly start filling using the bulk truck nozzle. Cover your fuel filler nozzle with a cap.