Quote: "I say again, drain the tank for long term inactivity and storage, especially if one's tank has a history of becoming contaminated with the typical fungals that easily clog 'filters'. Trucks and other vehicles that constantly refill their tanks dont have such a problem as do boats that sit around for weeks and months with 'stagnant' tank oil thats vented to the atmosphere.

Been draining for years and years and zero water in our tanks, ever. When we had to replace the tank on our current boat it had not been out in 32 years. The pick up was 1.25" off the bottom of the tank. When I cut open I poured what was left into a decanter and let it sit for multiple weeks. There was no water separation what so ever, just fuel. 32 year old tank with a pick up over 1" off the dead bottom yet zero water in it....

Our 275 gallon oil tank has a 1.5" diameter vent and suffers massive temp swings being in a heated, then un-heated, then heated then un-heated garage.. It is rarely if ever "full" for long. This entire summer it has been below 1/4 tank with RH here on the cost often in the 90%+ range. It has been installed since 1978 and to this day still has zero water in the bottom.

I am a believer that the cause of most water in fuel tanks is from leaking deck fills or a poorly placed vent line outlet. I had one boat at a marina that had a brand new fuel tank, new fuel fill and vent hose and a new deck fill. Within 6 months I noticed water in the fuel filter bowl. I was pretty stumped but tried a little experiment....

During the next rain storm I disconnected the vent line at the tank and stuck it into a glass jar. Sure enough the wind driven rain was entering the fuel vent on the transom and draining into the tank. Perhaps a 1/4 of a shot glass per storm if the winds were right. After a rainy spring there was enough for it to get picked up by the fuel pick up and make it to the fuel filter. I reconfigured the vent termination, drained and died out the tank, and it has been bone dry since...