noun
combined sewer
Technical term in civil engineering and urban infrastructure for a sewer system that carries both sanitary sewage and stormwater in a single pipe.
合流渠は、雨水と汚水を同じ管で流す方式です。
A combined sewer is a system that carries rainwater and wastewater in the same pipe.
Compound of 合流 (confluence, merging) and 渠 (ditch, channel, conduit). The exact historical derivation is uncertain; the term is a modern technical coinage.