Dispersion in sewers affects the concentration of pollutants within urban drainage systems and the quest to understand it has led to extensive studies of the hydraulics within circular manholes. Since there are both circular and square manholes within the urban drainage system, it is important to understand the hydraulics within a square manhole, its similarities and/or differences. This research is aimed at describing the transportation and mixing of soluble pollutants through urban drainage systems and the effects of structures such as manholes. It also seeks to study the relationship between headloss and dispersion coefficient in a full flowing pipe. Laboratory solute transport studies were carried out on a straight pipe with two diameter sizes (35 mm and 25 mm) of orifice plate inserted. Two square manhole sizes (388 mm x 388 mm and 150 mm x 150 mm) with a straight through flow was also studied at surcharge and overflow conditions. A relationship between the total headloss along the length of the pipe and the dispersion coefficient was established. With the introduction of a new parameter, a relationship was also established between the headloss due to the orifice and the dispersion coefficient when an orifice plate is inserted along the line of flow. It was observed for the large manhole size that at low surcharge depths there was more mixing occurring while at high surcharge depths the dye travels in a straight jet with some tracer trapped at the upper manhole volume. There exists a transition zone between the low and high surcharge depths which is not evident in the small size manhole. These observations mirror the phenomena that have already been observed in circular manholes. Manhole overflow studies was indicative of a completely mixed flow for the large manhole whereas for the small manhole it suggests a piston flow (sometimes referred to as plug flow) with some longitudinal dispersion occurring.