Stormwater drainage systems are often used to regulate stormwater runoff from urban areas. These systems should ensure effective stormwater drainage from urban areas, both quantitatively (preventing flooding) and qualitatively (reducing pollutant loads discharged into natural receiving bodies). In the near future, requirements and standards for protecting surface waters from stormwater runoff will become more stringent. This will necessitate the expansion of existing stormwater drainage networks with stormwater pretreatment facilities. The main pollutant in stormwater is suspended solids, which also carry other pollutants found in stormwater runoff.To ensure adequate surface water protection, the discharge of untreated stormwater into receiving bodies should be limited. Settling tanks are the devices whose primary function is to retain as much suspended solids as possible. Stormwater drainage systems should be designed sustainably. However, they cannot be implemented everywhere, primarily due to dense urban development or unfavorable soil and water conditions. Therefore, the development and modernization of underground systems, primarily by increasing their retention capacity, remains a significant engineering challenge. This article presents a device for pretreating stormwater (rain or meltwater) before its discharge into the receiving body. The device combines the functions of a settling tank and a retention reservoir. The proposed design is primarily used in stormwater drainage systems and wherever stormwater management is needed.