With any vinyl tubing, select material with greater wall thickness as opposed to thin wall thicknesses. This helps prevent kinking and collapsing, the two primary downfalls of vinyl tubing. Avoid placing heavy objects on tubing and be wary of burying it in deep excavations. Despite its limitations, vinyl works well when used in situations consistent with its capabilities.

As the pump flow-rate increases, the need for larger diameter tubing arises. For diameters larger than one inch (2.5 cm), a pond builder has two basic choices -- rigid PVC pipe and flexible PVC tubing. They handle large-volume water circulation. Flexible PVC tubing uses either glued or non-glued fittings. Environmental conditions, complexity of the plumbing system, pipe lengths and budget all influence the choice of rigid or flexible PVC.

Since pipe diameter largely dictates flow rates, picking rigid or flexible PVC may not seem much of an issue. However, it becomes an issue when you insert fittings into the equation. Flexible PVC readily bends, eliminating curved fittings that rigid PVC requires. Each fitting adds to the total dynamic head, reducing the output of the pump at a given height. In addition, flexible PVC comes in lengths up to one hundred feet (30.5 meters) in the US, eliminating coupling pieces of pipe together on long runs.

Another advantage of flexible PVC comes from its elastic structure. In cold weather regions, flexible PVC withstands freezing conditions that would rupture rigid PVC. While I do not recommend allowing any piping system freeze with water in it, flexible PVC is more forgiving. It also can tolerate heavy loads placed on the pipe, so you can bury flexible PVC without worries of damage.

While ideal for many jobs, flexible PVC does cost more than rigid PVC. Flexible PVC that incorporates barbed fittings to make connections is less expensive than the glued fitting pipe. However, the downside is thinner wall thicknesses, less selection of pipe diameters and the hassle of switching between barbed hose fittings and threaded component fittings. Fittings are potential leaks if not installed correctly. Barbed fittings combined with hose clamps are far from foolproof. Finally, the curved nature of flexible PVC presents problems when making connections on short, straight pipe runs. Patience and a heat gun help, but beginners should understand some plumbing jobs might require professional help.

For many water gardens and koi ponds without complex filtration systems, flexible PVC may seem a logical choice. Nevertheless, in applications with multiple filters, bottom drains, settling chambers and manifolds to direct flow to the proper destinations, rigid PVC gains the upper hand. Plumbing a filtration system with multiple components usually involves fitting a maximum amount of equipment into minimal space. Short pipe runs, tight clearances and sharp angles necessitate exacting precision, which rigid PVC delivers. Most hardware and home centers carry a wide assortment of rigid PVC fittings and pipe diameters suitable for water gardens and koi ponds. Just like flexible PVC, working with rigid PVC requires basic plumbing knowledge and skills. Do not be afraid to seek knowledgeable help. Ready availability, ease of use and low cost all steer many beginning ponders to the rigid PVC aisle.

Rigid PVC does have limitations. Exposed piping tends to be difficult to disguise, especially around a pump or filter located within the pond. As mentioned, rigid PVC may crack or shatter under pressure of copingstones or from being buried. Ground heave presents another concern when burying rigid PVC. Most damage occurs at fittings. Finally, extreme environmental conditions such as high temperature, UV exposure or extended freezing periods may cause early failure of unprotected rigid PVC.

Despite their differences, all tubing types share some things in common. Flexible and rigid PVC use the same glued fittings while vinyl and non-glued flexible PVC use the same barbed fittings. Any system benefits from check valves, ball valves, unions and quick couplers to make maintenance and repairs simpler and to improve overall performance. Always use the largest diameter pipe the system might require, just in case you later add an upgraded pump. Lastly, research suppliers for quality, warranty, service, reputation and knowledge as well as price. Like other pond materials, pipe quality varies greatly among manufacturers.