Quote Originally Posted by DrTimPerkins View Post
Although that could happen, it seems like a fairly unusual (at least not common) type of thing. Seems like perhaps your mainline either runs through a really cold spot or maybe has a high spot somewhere that doesn't allow it to drain properly. Either way, yes, it could result in backflow. However, keep in mind that if the trees are still thawed and sap is running then it means that there is PRESSURE within the tree for a good period of time as the lines freeze up, thus there should not be much of any sap moving backward at this time.
Yes, there is some cold spots, BUT its not b/c the line has a dip in it. Doesn't help that there is only 2% slope in some areas. I have seen my other woods with a 500 ft. section of mainline, north side @ 2% slope with icicles hanging off practically EVERY saddle, and red maple taps that were untapped and capped off (end of season 2016) at the T blown off in the morning up to 50 ft from the mainline. Conditions prior to this were a HEAVY run day which continued right into the night when it froze up hard and fast. No possible way those lines will drain under these conditions. And like most of us, the releaser and tanks are located in the area of the bush that will freeze up first.