main line closed or open?

[lakeview maple]

Im running my main lines for the first time on a pretty steep grade,its like goat country but on a nice east slope.My question is should I close the end on the line or leave it open,I was going to leave it open with just a screen or something on the up hill end to keep little critters out,but Ive read about natural vaccum.Im kinda lost so any help would be great thanks.Al

[whalems]

Close the end.

[red maples]

close it. the sap may seem like it is stuck in the line the trees will push it out along with the natural gravity vacuum helping to pull out the sapfrom the trees. if the end is left open the extra added air will help your taps holes dryout or closeup quicker ending your season earlier or just provide less sap toward the end of the season.

[kiegscustoms]

Another place to introduce bacteria. Granted it is open at the bottom but if bacteria enters at the top it will pass by every tap hole letting bacteria possibly back flow into the tap holes, causing them to dry up quicker.