The main purpose of pond tubing is to work in conjunction with the pond pump to circulate water from one portion of the pond to the other by pushing water up to a filter, a waterfall, a stream or even a fountain or water spitter.
The interior diameter of the tubing affects the amount of flow at a certain rate of water that can pass through the hose. A larger diameter hose will be easier for a pump to push water through resulting in more flow, less friction and less head height then if a small diameter hose is used.
There are several types of hoses such as PVC Hose, Non Kink Spiral Tubing and Vinyl Tubing. Depending on your application will determine the best hose for your pond.