Final answer:
Oil circulates back to the storage tank through the return line (option 2), which is separate from supply, vent, and drain lines. Pumps are used to overcome gravitational potential and provide kinetic energy for fluid flow, as in the case of a pipeline supplying water to a hilltop house.
Step-by-step explanation:
The storage tank system in the question involves different lines for various functions. Oil circulates through the piping system back to the storage tank through the return line. The supply line is responsible for delivering oil from the tank to where it's needed, while the vent line allows for the escape of built-up gases inside the tank. The drain line, on the other hand, is used to remove oil or other substances from the bottom of the tank during maintenance or in case of contamination.
In the context of water flowing through a pipeline, as in the example provided, a pump is necessary to create the pressure needed to move the water. If the end of the pipeline is open to the atmosphere, and the house is located 150 meters above the source, the pump must overcome the gravitational potential energy as well as provide enough kinetic energy for the water to have a flow rate of 5.0 m/s.
Drawing water in through a lower valve and out through an upper opening, as mentioned in the example of flushing a ballast tank, is another application of fluid flow where gravity and pressure changes are crucial for the process to work effectively.