1. A sap-collecting system for collecting sap from a plurality of sap-producing saplings having respective stems each having a cut top end, comprising:a plurality of sap-collecting devices operably disposed one each over respective top ends of the stems to form a vacuum-tight seal, each sap-collecting device having an interior and a first access port;
a line system operably connected to the first access ports;
a vacuum system operably connected to the line system, with the vacuum system including collecting tank, wherein the vacuum system is configured to apply a partial vacuum to each of the interiors of the sap-collecting devices so that sap flows from the top ends of the stems, through the corresponding sap-collecting devices and through the line system to the collecting tank; and
wherein the sap-collecting devices each include:
a flexible bag sized to fit over the top end of the corresponding stem;
at least one securing member configured to secure the flexible bag to the corresponding stem portion and to the end cap to form the vacuum-tight seal; and
a spacer configured to space the flexible bag away from the top end of the corresponding stem.