How does transferring of liquid in a container to an empty container using a plastic tube works?
You're talking about a siphon. You suck on the end to get the liquid up the tube and then down the other side, and all you need to do to keep it flowing is make sure the outside end of the tube is lower down than the inside end. The liquid pulls on itself, and there is more weight on the outer tube than the inner, so it's enough to draw the liquid up and down, as long as it ends up lower than it was before.
A siphon hose used to draw gas from a car's fuel tank is one example and is a very simple pump. Sucking on one end of the hose creates an area of low pressure compared to the relatively high-pressure area of the gas tank. This low pressure versus a higher pressure is key to the transfer. Eventually, the gasoline will come out of the low-pressure end of the hose and the process feeds on itself so to speak via momentum, and the fluid continues to transfer.
