Originally Posted by boatpoker
Vents should be connected to throughulls well above the waterline, as close to the sheer as possible.
You may be right and I don't know if there are any specs that agree or disagree with your comment but...
I would never run my freshwater tank vents topside because saltwater or harbor water contamination may result. My vents are all loops of hose that run from the tank to very high under the deck
then back down toward the bilge
...ending well short of the bilge to allow drainage to it but prevent contamination if the bilge is full and the boat is heeled or suffers a knockdown.
Fresh water in the bilge hurts nothing. Harbor water or salt water
in the tank can hurt your tummy.