In fact, volume is not a new concept. We have consulted relevant materials. As early as the beginning of this century, the volume expression was used in describing the design principle and relevant parameters of the three compartment septic tank toilet in the rural environmental sanitation work guide and the Chinese rural sanitary toilet guide. Because for the three format septic tank, only the part passing through the lower edge of the fecal pipe is the actual storage space of fecal sewage, and the part passing through the fecal pipe is a cavity, which does not store fecal sewage. In this regard, the "sanitary code for rural household toilets" proposed three compartment septic tank volume �� 1.5m3 refers to storage space. "Plastic septic tank" clearly uses the volume. In 2019, the requirements for the construction of rural household toilets (Trial) issued by the public health department and the Ministry of agriculture and rural areas re emphasized the volume in the three format household toilet structure.

Judging from the current situation, some places do not understand this. If the total volume of the septic tank is used to replace the volume, the space for harmless treatment of fecal sewage will be too small to achieve the effect of harmless treatment of fecal sewage within the specified residence time. Therefore, the standard released this time clearly uses the volume expression, which helps to ensure that the fecal sewage achieves the effect of harmless treatment. At the same time, the standard also gives the reference value of the septic tank volume in combination with the family population: for less than 3 people, the reference value of the volume �� 1.5m3�� 4-6 persons, volume reference value �� 2m3�� 7-9 persons, volume reference value �� 2.5m3, convenient for local selection.