I have 2 "poly-cube" fuel tanks on my boat.They are portable, 15 gallons ea. Poly cubes are pretty much just heavy duty general purpose tanks, not your standard fuel tanks. Very popular up here for folks making long runs up rivers where they need added fuel capacity. Anyway, they use standard 55 gallon drum style, plastic bung caps. They aren't vented and the other day I went on a pretty long run in the boat and noticed the sides of the tank were sucking in from the vacuum. I know this could cause problems, but I can't for the life of me find any vented caps for the tanks. Any idea where I can find a cap that would allow for ventilation without letting water in? <br />Thanks- Steve<br /><br />By the way, the Attwood vents for sale here at the Iboats Mall are what I will probably go with, if they will keep out the water. Unless you guys can think of a replacement cap? Any suggestions?