Cleanout systems are disclosed. An example environmental control system includes an exhaust plenum to exhaust cooling fluid from a heat exchanger outlet of a heat exchanger, and a cleanout system coupled to the exhaust plenum adjacent the heat exchanger outlet. The cleanout system includes a cleanout passageway to fluidly couple a cleanout inlet accessible from an outer surface of the exhaust plenum and a cleanout outlet in fluid communication with the heat exchanger outlet. The cleanout system is to enable removal of particulate from the heat exchanger without disassembling the heat exchanger from the exhaust plenum or an air intake.