Most of the schools, offices and companies work in a single shift, schools even if there are 2 shifts the schools is closed for 12 hours. This has a direct connection to the amount of water comes to the wastewater treatment plant as all the water come to the plant collection tank in just 12 hours and has to treated in a day or 24 hours period.Sizing of the collection tank should be according to this. There are many failing sewage treatment plants due to badly sized collection tanks. As a rule of thumb, for a school or a single shift operation the collection tank should be at least 1 day to 1.2 days flow volume.