Fuel tank suction

[bigmac]

I'm pretty sure (can't find the reference) that NMMA rules require fuel tanks be vented to the outside. Obviously they also have to vent in to keep negative pressure from building in the tank. USCG and NMMA do require that all fuel tank venting be to the outside of the boat - not into any closed compartment.

As I understand posts about problems with these Perko "gas fill and vent" fittings, that two way venting is done through the filler cap.