Seems the vent line being a larger inside diameter it would take an aweful lot of water to form a vaccum strong enough to suck the water around the loop. More water than could get in at one time - unless it went UNDER the water - then you got lots of other issues!

All I know is I've heard others say it and my V21 has a big ol loop in it above the vent. Factory I assume since the vent hose is pretty old and decrepid looking.

Oh man, gotta read this.....some people apparently got into it on THT over whether a loop would trap or drain water from the vent. Some nasty name calling LOL!!!
http://www.thehulltruth.com/archive/t-388463.html

I still think a loop done the right way would never allow water in the tank under normal circumstances.

A lot of the new boats are coming with a flush mount fuel vent. It's 316 stainless and 90 degree. I'm not the best at posting pics but the Sea-Choice part number is #50-23061 and should sell for @ $25. It's probably a Perko.