A cleaning machine has a housing, a supply tank, a suction nozzle, a suction source, and a recovery tank that includes a container having sidewalls projecting upwardly from a bottom wall thereby defining an open top, a cover connected to the open top of the container, and an air-liquid separator extending into the recovery tank from the open top and having a vertical sidewall, a lower wall extending laterally from a lower end of the vertical sidewall toward an adjacent sidewall of the sidewalls of the container. The vertical sidewall, the lower wall, and the adjacent sidewall define a separation chamber, the vertical sidewall includes a vertical rib extending outwardly from the vertical sidewall and into the separation chamber. The separation chamber includes a dirty fluid inlet receiving fluid from the suction nozzle through the cover, and a dirty fluid outlet directing fluid from the separation chamber into the container.