Plastic pipe comes in the same diameters as metal pipe. Special adapters and fittings connect plastic pipe with a metal system. Plastic is chemically and electrically inert and is smooth inside, so it will not rust, corrode, accumulate mineral deposits, or clog as readily as metal.
Plastic pipe comes in rigid and flexible varieties. What you will purchase depends upon the plumbing code in your area and on the function the pipe and fittings must serve. Rigid pipe can be used for either drain-waste-vent (DWV) or hot and cold water-supply systems, depending on the type of plastic. Flexible pipe is only used for supply systems.

Rigid pipe is cut with a hacksaw and is glued together with solvent cement. Most codes specify that pipe and fittings of different plastics cannot be mixed in the same system. The materials require different cements and expand at different rates. A typical do-it-yourself project, such as hooking up a new sink, might use rigid CPVC (chlorinated polyvinyl chloride) pipes for the hot and cold water-supply lines and rigid PVC (polyvinyl chloride) for the drain line.

Flexible pipe is joined with compression fittings rather than solvent cements. The most common flexible pipe, PB (polybuty-lene), is used for both hot and cold interior and exterior water supply systems. It has excellent heat resistance and is very strong, but is generally more expensive than rigid pipe.
Flexible pipe is particularly suited to remodeling jobs where pipes have to be snaked through walls, floors and ceilings, and to lawn irrigation systems. Although this pipe is flexible, it can kink and should be bent only into gentle curves. It is rigid enough to support itself on fairly long runs but it is best to use extra supports.

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