Please confirm that I'm correct in the advice to others (some outside the
newsgroup) that there is no point in filling the tank unless it's filled up
into the vent so that the surface area of fuel available for water vapor
transfer is the cross section of the vent pipe and not the whole top of the
tank.

Since this is impractical in many vessels and impractical in most normal
operation, the whole topping up the tank thing is a crock.

I'm going to put a desiccant vapor trap on my sounding tube for the winter
which is easy to do and tape over the vent.

--
Roger Long

Here's a website that gives a brief tech description of what is
happening .... sorry that its JetFuel but the same happens with
diesel, etc.:
http://www.flowmeterdirectory.com/fl..._07082401.html

My professional (filtration engineering) work in this area has
included the ultra-pure ultra-dehydrated oils used in high voltage
transformers, contactors and tap changers ... although sealed,
eventually become contaminated with water (free, dissolved and
emuslified) which radically changes the dielectric strength of the
oil. The water uptake is all by 'chemical equilibrium'; you put in
ultra-dehydrated oil - come back in 2-3 years and remove the water
( or replace the equipment if if shorts out due to the water and
generated particles). Simple physical-chemical equilibrium at work.

Bruce reported using oil that was barreled in WWII. Entirely possible
if the barrel was filled at temperature that sterilized the contents,
is totally sealed, no water entered, and no fungal spores got in.
After all, that oil is zillions of years old and it stayed in the
ground because no microorganism used it as a nutrient source, etc.