Final answer:
An overflow pipe or overflow tube is a vertical vent that prevents a drain from overflowing.
Step-by-step explanation:
A vertical vent that is a continuation of the drain to which it connects is called an overflow pipe or an overflow tube.
This vertical vent serves an important purpose in preventing a drain from becoming clogged or overflowed. When the water level in the drain rises to a certain point, it will flow into the vertical vent instead of overflowing onto the floor or countertop.
The overflow pipe is typically larger in diameter than the drain to allow for a greater volume of water to be carried away. Its vertical position promotes a smooth and rapid flow of water.