PurePro®-Trilogy®-Triple Clean Professional™-OptiClean®- dust blowing from the lower hose.

Answer:  

Check for clogs in the lower hose.

Lay unit down on its front side so the lower hose is facing up. Remove two screws from the left side of the lower hose on back of the unit and straighten this section of hose by pulling it up straight. Look through the hose for obstructions. Push a broomstick through the lower hose to unclog. The debris will fall out from the brush area. Throw large debris away in the garbage and vacuum the immediate area.