You will be ok venting through the filler tube I blocked my tank vent and pump had a vent tube aswell, I ran mine on the filler tube no issues . I use a flip top fuel cap. I removed that flip Over valve as I couldn’t locate it high enough under the car and when I filled it with fuel It would spill out of it and I didn’t want to place it in the boot due to vapours . Just make sure that steal breather isn’t blocked on your filler tube.
