Overflow would be an issue, but the idling vehicle would be about the same risk as the idling fuel truck if you buy from the FBO.

Charlie

Probably the simplest approach would be to get a good measure of the flow
rate, and then just carry a little timer to alert you to when you've pumped
the amount you want.

Then you have to have some sort of 'shutoff'' at the end of the hose so it
doesn't drip all over when you're finished.

Al