Pipes and fittings allow water to flow into your backyard waterfall. The valves let you manage the route and rate of that flow. Most of the plumbing supplies can be provided by plumbing stores, home centers, and garden dealers. By choosing the right size of pipe, fittings and valves you can make pump work most efficiently. When planning your pipe directions remember, water flows best when it runs straight. Find pipe with a smooth bore, and make least sharp turns in the layout.   Copper tubing should not be used for backyard waterfall. Plastic pipe and fitting are preferred for supply and drain lines. Plastic pipe is easy to cut, assemble, and very affordable, unlike copper and other metals, it will not rust outdoors. Several different types of plastic pipe and fitting are available.   Flexible pipe is the easiest to assemble and install. If you need to put rigid pipe, look for schedule 40 PVC, (polyvinyl chloride) which is joined with solvent fittings.   Corrugated plastic pipe costs more than other plastic pipe, but it can be bent around obstacles without kinking, it can reduce the time for installing fittings.   For waterfall, from 1/2-inch to 1/4-inch pipe will be enough. To more...