GM Diesel capless filler plug

Went to fill my DEF tank the other day and stuck the DEF nozzle right in the cap-less filler for diesel fuel.  Fortunately, I caught myself before I was forced to learn an expensive lesson.

I thought a plug to go in the capless filler hole might force me to take a second to think before sticking a nozzle where it doesn't belong.

I printed this out of TPU, and it fits snugly.

I'm not sure if the vent hole is necessary, but thought it was better than not having one at all.