Steven, This is a pic of my solution for venting an outboard (above deck originally) tank. from left to right is the modified filler cap with a brass fitting screwed in and sealed, metal garden hose cut-off insert, plastic hose barb fitting for 3/4 hose, brass thru-hull fitting. The only change I want to do in addition to this will be a way to close the thru-hull fitting a bit smaller(1/2 opening at the moment). Tank filler cap-$10. all other hardware $8 total. spare garden hose length.