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a structure in a sewer network used for inspecting, cleaning, and flushing the sewers.
The manhole usually consists of a work area and, above it, an entrance area, a hatchway, and a lid. There are inspection manholes, drop shafts, and flushing shafts. Among the inspection manholes there are line shafts, built at straight sections of the sewer network; corner shafts, where the line changes direction; juncture shafts, where several lines come together; and control shafts, where the networks draining individual buildings or city blocks join the street network. Drop shafts are built where there is a substantial difference between the levels of the delivery pipes and drain pipes. Flushing shafts are used in flushing out the sediments that form in pipes carrying effluents with a slow rate of flow.
In cross section, manholes are either round or rectangular. They are built predominantly from prefabricated reinforced-concrete rings and panels. Sometimes they are brick.
IU. M. LASKOV