Basic SEWER Plumbing Wastewater flows through small lines on your property to the larger, city lines in the street. From there the sewage travels by gravity to a wastewater treatment facility. The stream is constant, with peaks in the morning and evening. Each day millions of gallons of wastewater safely reaches Trinity River Authority’s treatment facilities to be reclaimed and returned to the environment. The City of DeSoto purchases wastewater collection and wastewater treatment services from Trinity River Authority.