The cleanout cover system of this invention is operable with a container having a reciprocating slat-type conveyor for supporting and moving particulate material rearwardly at an unloading site. The container has laterally spaced side walls and a front connecting wall, the rear end being operable for unloading. The cleanout system includes a flexible cover sheet spanning the distance between the side walls and an elongated strap connected at one end to the center point of the front end of the cover and at its opposite end to a strap wind-up reel powered by a pneumatic motor. The reel and motor assembly is mounted on the container adjacent the upper end of the front wall of the container centrally between the side walls. A brake system associated with the reel serves to prevent unwinding of the strap when the pneumatic motor is deactivated after the strap is wound fully onto the reel with the cover suspending therefrom and permit unwinding of the strap when pulling tension is applied by the cover during unloading operation of the reciprocating slat-type conveyor of the container.