This saves the labor of going to each tree periodically to empty the buckets. In this method, the taps are called spiles. The vertical lines that connect the spiles to the branch line are called drop lines. These lines allow the spiles to be moved to new holes around the tree each spring without re-plumbing the line. These lines also allow for the separation of CO 2 gas and sap.
All plants use carbon dioxide to live.
A large part of what comes from the taphole is CO 2 gas which, if not separated from the sap, can contribute to vapor locks, inhibiting the flow of sap.