Abstract: A sewer lateral cleanout apparatus provides visual indication of an impending sewer backup, for installation on the cleanout riser of a sewer lateral, and includes a housing portion adapted for attachment to the cleanout riser; and a vertically movable piston portion slidably engaged within the housing. The piston includes a float member, a wall member, and a cap member, such that when sewage is not backed up into the cleanout riser, the wall is contained within the housing, and when sewage backs up into the cleanout riser, the float urges the piston to move vertically within the housing to reveal the wall, thereby alerting the user of a backup.