The emblem in the centre of the cover consists of two parts: the emblem of the city of Tokyo in the middle, surrounded by a stylised frame representing the kanji 下水 (sewerage). The emblem as a whole is associated with the Tokyo Metropolitan Sewerage Bureau.
This design, known as "下水構え" (sewerage frame), originated as part of the emblem of the Tokyo Municipal Sewerage Bureau and also appears on sewer and drainage covers in other Japanese cities. One example is a cover found in Morioka