The Two-Pipe System
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A soil and waste system comprising two independent pipes, namely, a soil pipe conveying soil directly to the drain and a waste pipe conveying waste water to the drain through a trapped gully*. The system may also require ventilating pipes. Soil is defi ned as the discharge from water closets, urinals, slop hoppers, stable yard or cowshed gullies and similar appliances. Waste is defi ned as the effl uent from a waste appliance. The latter is defi ned as a sanitary appliance for the reception of water for ablutionary cleansing or culinary purposes and its discharge after use, e.g. wash basins, sinks, baths, bidets etc. (BS4118). Notes on the Two-Pipe System. This is the traditional system used in the U.K. and has always been regarded as being simple yet certain, although costly. It is suitable for buildings (all types) which have sanitary appliances widely separated and close grouping together around one mainstack is impracticable. Even at the design stage, this system can become complicated due to the number of pipes involved, viz: soil pipe, waste pipe, often two main ventilating pipes and sundry branch soil, waste and anti-siphon pipes. Before the introduction of Building Regulations, hopper heads could be used in certain positions (if permitted by L.A.) and certain branch waste pipes could then simply discharge into a hopper head. As Reg. N5 requires soil and waste pipes to be internal, hopper heads are no longer permitted for waste drainage. Due to internal fouling, hopper heads can be a source of nuisance and their elimination is welcomed.