Regarding Christopher Zavatson's alternate tank vents, it's a darn good
idea! I've done the same thing (main vents tee'd into check valves) but for
an entirely different reason.

I posted this a while back but here it is again in a nut shell. During a
test flight, I was transferring fuel from the left wing to the header.
Luckily, the light was just right and it allowed me to noticed that the left
wing skin was showing a slight negative deformation, enough for the rib
outlines to be seen in the glancing light. I had never seen this before so I
quit pumping fuel and got on the ground, pronto. I knew it was a plugged
fuel vent but nothing was visible on a ground inspection until I ran a piece
of safety wire into the vent. Turned out that a wasp of some kind had taken
up residence about a half inch into the vent tube, completely blocking it
with mud and completely out of sight.

If I'd have continued pumping fuel out of that wing, I have no idea whether
the pump could have overcome the structural integrity of the skin or whether
it (the pump) would have stalled before damage had occurred. Regardless, I
had no intention of finding out so I added the check valves. To guard the
check valve's inlet, I wrapped a couple of layers of cheese cloth over the
inlet and fastened it with a loop of safety wire. No pressure recovery from
the valve inlet as they're inside the wheel wells (for the wings and behind
the panel for the header) but no collapsing wing or header tank due to ice
or bugs, either.

Incidentally, if I have to leave the airplane outside for a while, like on a
trip, I now stick some real fluffy pipe cleaners into the vents to
discourage the local bug population from hitching a ride in my fuel vents.
The ends that stick out are colored red so I don't miss them during
pre-flight (though if I should, the check valves will keep me out of
trouble).

Dan Schaefer