And if you gas up at a marina for gas and spill a little, over comes
the nice dock helper with a bottle of detergent, sprays it down and
the gas sinks to the bottom - it's doesn't go away, it just sinks.

Whenever I fuel up, I get a free bio-diaper from the fuel dock. My fuel system
is located so I can hold the diaper at the vent and operate the nozzle at the
same time.
While fueling, I listen carefully for the sound of fuel just beginning to
gurgle in the vent line, and that's the point at which the tank is considered
"full" and fueling stops.
If I fail to hear the gurgling sound and a teaspoon of diesel does come
shooting out the vent, the diaper will catch it.

If the vent were some distance from the deck cap, it wouldn't be all that tough
to ask my wife to hold the diaper at the vent, or even tape it in place when
running single -handed. Several companies make devices to catch any fuel
accidentally forced through the vents, and much like anything else they sell us
for boating some of the designs probably work better than others.

If the dock boy needs to come running with the detergent bottle, I would submit
that there may be room to improve the fueling procedure.

A few ounces of fuel can spread over a wide surface area, and that's just the
sort of spectacle that doesn't do our public image a lot of good. :-)