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Sewage management is important in the development of an area. The method used should be cost effective and environmentally friendly. Traditional methods used for sewage collection in Kikuyu Town include insanitary pit latrines (used by households) and septic tanks (mostly used by industries and institutions to cater for the large volumes of sewage). The best alternative is a sewerage system that uses sewer-lines to convey sewage into a treatment works. This project seeks to replace the traditional methods currently used in Kikuyu Town with a sewerage system. Geospatial technologies are used to site a treatment plant and the main trunk sewer-line route in Kikuyu Town. A comprehensive methodology that incorporates environmental factors is adopted. These factors are weighted using the Analytic Hierarchy Process (AHP). The most crucial factor considered in this research from weighting is slope, as the sewer line is designed to flow by gravity. The objective is to have the sewer-line on sloping terrain from high to low elevation areas, where the treatment works is located. ArcGIS is used to analyse these factors to determine a feasible route for the main trunk sewer-line. This produce an optimal route that avoids forest cover and water bodies. Road crossings and rail crossings are also minimised. The proposed route utilises the existing road reserves, which help in minimising the costs while also reducing disputes that may arise due to acquisition of private land.