A bar sink overflow tube is a small opening in a sink with a tube of various heights fixed into it. The holes on top of the tube attract water once the sink is full up to that level. Then the outlet connected to the drain at the bottom lets the water flow down the drain.
During warewashing operations, it is common to block the sink drain with a drain stopper and fill the sink with water. Sometimes, it is also possible that water flows very slowly through the drain due to food particles. By redirecting the water into the drains, overflow tubes prevent flooding. Also, a bar sink overflow tube ensures faster water drainage by allowing air into the drainpipe.