The article is devoted to increasing the efficiency of using devices for dosing reagents in oil pipelines. The object of the study is a downhole reagent dosing unit designed for a controlled supply of reagents into an oil pipeline or a well. Malfunctions during the operation of installations of dosing devices are analyzed. The article solves the urgent problem of increasing the efficiency of the dosing device by cleaning the supplied chemical reagent from mechanical reagents through a fine filtering device. The design of a fine filtering device as part of a downhole dosing unit is proposed. A 3D model of the filter has been created. Strength analysis by the finite element method in the ANSYS Mechanical software package showed that the maximum stresses arising in the filter do not exceed the maximum permissible stresses. Industrial tests of the fine filter gave the following results: removal of mechanical filters was reduced by three times; the possibility of multiple uses of filters after flushing was achieved, while the pump failure time increased to 100 days, and the wells operating time increased to 500 days.