The accumulation of fat, oil, and grease (FOG) deposits reduces the hydraulic capacity of sewer networks and ultimately leads to sanitary sewer overflows (SSO) or combined sewer overflows (CSO). To investigate the impacts of suspended solids on the formation of FOG deposits, systematic experiments were conducted in beakers. Oleic and palmitic acids were used as the typical unsaturated and saturated fatty acids, respectively. It was found that the total weight of FOG deposits increases with increasing flow velocity due to the increased mixing. The suspended sand can lead to a significant decrease in the weight of FOG deposits at a relatively low velocity gradient (G < 221.0 s–1), but its impact gradually diminishes with increasing G. The solids formed from palmitic acid are more adhesive than those from oleic acid. There is a pronounced spatial variation in the percent saponification (S) of the FOG deposits: S is notably higher near the concrete surface and decreases toward the outer layers.