3/16 tubing sap collection vent?

[LMP Maple]

trying my hand at 3/16 this season. I purchased 55 gallon sap barrels from Bascom that have tops that come off and are held on with a lever type clamp. I ran all my runs on Sunday and will be tapping tomorrow. My plan was to run the line through the top of the barrel and have read many threads on this to be sure to make it a tight fit for the tubing etc. One thread mentioned that you need to have a vent line. Just wondering if this is necessary? I know a head tank can get vapor locked if the cover is too tight but I thought that was because you were removing liquid from the vessel. The concept makes sense when adding sap to a closed system as the air would have to go somewhere just wondering want other people think or do to vent there storage containers if at all.

[Ghs57]

I did the exact same thing for a few years about 5 years ago. Same drums, except I was on 5/16 at the time. I never really locked down the lid though. When I switched to 3/16, the holes were oversized, so it ws not airtight. I still use the drums in a few locations, but never have an airtight seal on the lid or tubing. Same with my IBC totes.

[wmick]

I'm really not sure why it would need to be "tight fit"? To keep rain and bugs out maybe? You will need to allow air to escape as sap enters. You don't want to create any back pressure. Just be sure to keep the end of your sap lines up out of the sap.... so the trees don't draw it back out of your barrel at night.