Abstract
The purpose of the article is to specify and supplement the methodology of engineering calculation of rain runoff control at the treatment plant, given the current regulatory and methodological framework. Two flow management schemes, including an intermediate tank, a pumping station, and a separation chamber, have been analyzed by mathematical modeling. Changes in the calculation formula for determining the required volume for the tank connection scheme when emptying the tank by gravity are proposed. There is a significant difference in the calculation results according to the proposed and current regulatory methodologies.