...I even have a desicant filter in my tank vent. QUOTE]
Not to wander from the OP's thread subject, but this situation might apply to his situation, or others, storing large amounts of aux fuel in vented tanks...
I just purchased a nice used 50 gal aluminum Dura-Craft diesel truck tank (refer tank) that has a 90 deg vent elbow coming out of top with a short section of hose sticking out. I don't want to leave that open to the atmosphere to suck in moisture especially with our 5% biodiesel. I did a quick search for water absorbing filters and didn't find anything...my search kept giving me water separating fuel filters. So, do you "boatman" or anyone else have a
source for a desiccant type vent filter that I could attach to, or replace, this fitting (1/2" pipe thread into tank) somehow: