Hope this is OK for this forum - DEF question

I had the same problem until I figured out how to use the darn boxes...If you look at the plastic accordion spout that comes with the DEF box, you'll see next to where the spout exits the cap is a rubber piece with a slit in it, that's the vent that allows air in as the jug empties. The rubber slit has to be ABOVE the spout, regardless of how the box is oriented to the spout.

See here in this photo:



The vent slit is the black piece on the cap next to the base of the spout. the jug on the left you would hold somewhat "normally" when filling the tank. Now look at the jug on the right, you would need to hold it sideways to keep the vent ON TOP of the spout position.

Seems like the orientation of the vent is different on every jug when you screw the spout on. Just be sure to hold the jug in whatever position keeps the vent above the spout and you'll never spill a drop.

Ford makes one https://www.amazon.com/Motorcraft-NOZZLE-ASY-PM27N/dp/B008B5WVF8
as an example

A better forum might be tow vehicles.

I have found that EVERY SINGLE jug of the stuff I've bought in a year has the spout threaded in a way that the rubber vent is at the bottom and causes leaking like you explained. EVERY ONE. I have unscrewed and screwed them so many times thinking I was doing something wrong. Nope. The way they are manufactured the vent ends up in the wrong place. The only way I found to deal with it is hold the bottle upside down in the most awkward way possible.

I quit using the jugs and fill with DEF from a gas style pump at the fuel station.
It's cheaper, but more importanly there is no dripping or spilling.

No matter where you fill make sure you have some clean water to rinse off truck if needed. YES even at the truck stops as the nozzle still may not shut off or may burp some out.

Jamb the spout in fully and have the hose come away from the truck at a slightly upward angle with the box upside down. I never drip on truck this way. YES it may get a few drops on the ground, no biggie.

Should be moved to "Tow Vehicles".

Having the same leaking trouble, I got a $11 battery powered pump from harbor freight. Can set the jug on a stool, dip the pump and hit the switch. Takes about 2 minutes, no fuss.
The Pump

I use a cheapo plastic siphon that I bought at Canadian Tire for a few bucks. On my GMC, the DEF filler is under the hood, so I set the jug on the radiator cross member, one end of the hose in the tank, the other in the jug, squeeze the bulb a couple of times, and Bob's yur uncle. No muss, no fuss. Takes just a few minutes to empty the jug.

Put a lot of those Blue DEF jugs in my truck over 9 years and never had one leak except one time when I thought it was screwed on tight, and it wasn’t. It was cross threaded. Just make sure the spout is screwed tight and not cross threaded. Location of vent didn’t seem to matter.

truck stops that have def at the pump