I would personally NEVER use such a valve because I know, I just KNOW I'd forget it and make the internal mess discussed above above.

Rather, I use a simple plug in the vent line and attach this [link=http://dreamworksrc.com/catalog/product_info.php?products_id=1451]flag[/link] or this [link=http://dreamworksrc.com/catalog/product_info.php?products_id=197]flag[/link] to the plug with a bit of safety wire. Makes it difficult to miss the fact that the plug is still in, and when I did get ahead of myself during fueling just the other day, forgetting to pull it, the plug popped out all on it's own. No fuse mess from my forgetfullness, thank goodness.

On one recently completed jet I ran the vent straight out of the tail. If it exits at the bottom/aft end of the fuse there's little or no leakage in any attitude and what does dribble out does not tend to come into contact with the airframe.