Bubbles moving up line

[steve J]

When checking my garvity lines this morning I saw that one line appear to have bubbles moving up hill is there is explanation for this?

[buxtonboiler]

Sounds like air from your barrel coming up the tubing. Mine does the same thing, so I would say it is normal.

[TapME]

was the line frozen somewhere and sap was coming in and air moving up hill? just a thought.