Posted for Kevin Kossi <kevin@airforcemechanical.com>:

Chris,

I would think the volume of air flowing the tube would be equal to the
volume of fuel being drawn from the tank.
If there is water there, it could or would be drawn into the tank?
If the engine is using 15 Gallon per hour, at 231 Cu/In per gallon, thats
3,465 Cu/In per hour, divided by 60, thats 57.75 Cu/In per minute of air
being drawn through the tube.
I don't have time right now to calculate the speed of the air moving through
the tube in feet per minute, it its not zero.

Kevin

[The area of a 1/4" id tube is about 0.05in^2, so it would take 1155 inches of tubing to hold 57.75cf, which equates to about 96 feet/minute to move that much volume. Increasing the ID of the vent tube to 3/8" would reduce that velocity by more than 1/2 (its x-sectional area is about 0.11in^2. <Marv> ]