The development of a reliable methodology for calculating drainage pipelines in reclamation systems is crucial for en-hancing agricultural production efficiency and optimizing the use of water and land resources.Many existing calculation methods do not consider the simultaneous influence of pipe slope and groundwater level slope on the characteristics and operating conditions of collecting drainage pipelines. Addressing this issue will contribute to the advancement of modern hydraulic engineering and hydromelioration.The purpose of the article is to develop a methodology for calculating the parameters of pressure collecting drainage pipelines in reclamation systems, which are laid with a slope and operate in the presence of a groundwater level slope.A system of differential equations describing the liquid motion in collecting drainage pipelines laid with a slope and operating with a certain groundwater level slope is presented in the article. This system includes a variable mass hydraulicsequation and a modified filtration equation. The original system is reduced to a dimensionless form by introducing new vari-ables. The solution to the equations system results in straightforward and easy-to-use analytical dependencies for calculating the main hydraulic and structural characteristics of precast drainage pipes.The analysis employs the concept of an infinitely long drainage pipeline operating with a groundwater level slope, equivalent to an inclined pipeline with an infinitely filtering capacity of the side surface walls. The impact of drainage pipe geometric slope and groundwater level on its design charac-teristics is evaluated.The obtained dependencies for calculating collecting drainage pipelines will enhance the efficiency and reliability of drainage systems, improve resistance to extreme weather conditions, reduce energy consumption and enhance adaptation to various operating conditions