Foul drain

A foul drain is the section of underground pipework that carries wastewater containing human waste, food residues, detergents and other organic matter from a property to the public sewer or treatment system. It serves toilets, basins, baths, showers, kitchen sinks and washing machines, keeping contaminated flows separate from rainwater in most modern UK systems. Foul drains are typically laid at a controlled gradient with smooth-bore PVC-U or clay pipe so that solids do not settle and cause blockages. In London and other UK areas, design and installation must comply with Building Regulations Part H, which sets out minimum pipe sizes, ventilation and access requirements. Where a foul drain serves more than one property it is usually classed as a lateral drain or public sewer maintained by the local water company.