Europa-List: Fuel venting

[Fred Klein <fklein@orcasonline.com>]

I understand that some builders have vented the tank and the sight 
gauge to the top of the fuel filler pipe, taking care that the precise 
location will not allow fuel being added to inadvertantly flow into the 
vents. What I don't understand is...using the supplied fuel filler cap 
(which is specifically called out as "non-venting", again in the ACS 
catalogue)...how such an arrangement in fact can act to vent the fuel 
system.

Can anyone enlighten me?

Fred