Originally Posted by Jhayd11
How do you know when it is full?
When it stops flowing in. By using the bottle screwed into the fill port, because it is not very high, you will always be below the vent of the tank. If you fill using a hose from higher up (as in the picture at the beginning of this thread) you could overfill the tank and have DEF come out the vent which will only crystalize and possibly plug it.