Drainpipe

Drainpipe refers to a pipe that carries wastewater or surface runoff away from structures. In plumbing, drainpipes are part of the drain-waste-vent system and convey effluent from fixtures such as sinks, toilets, and showers toward a sewer, septic tank, or municipal drainage. In some regions, the term also applies to roof drainage pipes that carry rainwater from gutters to the ground or a drainage system; in those cases the term downpipe or rainwater pipe is common.

Materials and forms: Drainpipes are made from materials including PVC, ABS, cast iron, clay, or lead in older installations. Modern residential systems favor PVC/UPVC or ABS for DWV piping. Sizes vary; interior drains typically range from 1.25 to 4 inches in diameter, with larger diameters used for main stacks and external drainage.

Installation: Drainpipes are installed with gravity flow, requiring a steady slope so that waste moves freely. Horizontal drains commonly use a slope of about 1/4 inch per foot. Joints may be solvent-welded, glued, or mechanically fastened depending on material. Vertical runs often include traps, cleanouts, and proper venting to avoid siphoning.

Maintenance and issues: Blockages from grease, hair, soap scum, or foreign objects are common causes of slow drainage or backups. Leaks and corrosion may develop in aging systems and in exposed outdoor pipes during freezing weather. Regular inspection, prompt repair, and accessible cleanouts help prevent problems.