I use cv2 spouts on 3/16. I have a section of 5/16 at the end of each drop and then 3/16 to the lateral.

The trees do suck in sap when it starts to freeze even if you don't have vacuum - they get a tremendous negative pressure in the tree.

I'm in a combination vacuum + 3/16 system so it helps more than if it was just vacuum, but even in just gravity it can help in a year like this.