Wish I could say it was me in the Abacos, but it wasn't. As for posting pics, read this thread:
You might need 10 posts before you can post a pic though.
I'm at my boat right now looking in the locker and cannot find anything with a vented loop. Also, I don't have my camara with me, but let me describe the hoses I have and see if one matches with your mystery hose.
1 Forward end of the locker, scupper to drain
2. Metal piping from propane locker running along outer edge of locker to stove.
3. Diesel fill hose from deck plate to aft end and down to tank.
4. Manual bilge pump from port seat back to forward floor
5. Exhaust hose from transom to forward floor.
6. Blower motor hose from cockpit below port side seats near the wheel to foward locker floor.
My boat actually doesn't have the water tank vents, that's why that was my first guess.