This research focuses on the redesign of the sanitary piping system on a passenger ship that sustained damage due to a tropical cyclone in the vicinity of Bolok Port, Kupang. The main objective is to redesign the sanitary discharge system to comply with MARPOL Annex IV and classification rules, which governs sewage pollution prevention from ships. A structured engineering methodology was employed, encompassing adherence to regulations, hydraulic evaluation, selection of system components, and schematic design. The assessment considers the number of crew and passengers to determine system requirements. Based on the analysis, the vessel requires a sewage holding tank with a minimum capacity of 4,11 m³/h. Sanitary discharge piping is specified using DN40 Schedule 80 carbon steel pipes according to JIS standards. Jets STP 600 was chosen as the sewage treatment unit, offering a treatment capacity of 0,6 m³/h and conforming to the standards outlined in IMO MEPC.227(64). This retrofit design aims to improve sanitation efficiency, enhance operational safety, and reduce the environmental impact of wastewater discharge. These results provide a basis for the application of sustainable retrofitting strategies on vessels operating under comparable maritime environments.