A fast, convenient and user-friendly modelling tool was used to model biochemical and physico-chemical processes in the collection system. With this new tool two case studies were investigated with different scopes and purposes: one with a focus on the integrated modelling of sewer and wastewater treatment plants (WWTP) and the other aiming at a large-scale sewer network. Scenario analysis was carried out under different chemical dosing strategies. The work proves that processes in sewers can cause a significant impact on a downstream WWTP, and the wastewater treatment process can be better managed and optimized with the help of sewer-WWTP integrated modelling. The tool can also identify hotspots of key indicators like total dissolved sulfide in a large-scale collection system. It is suggested that investigating the network from a wider perspective can help target key issues and regions.