Noobie suggestion alert!!!!! You have been warned so someone speak up if this is a bad idea. I don't know what the ducting is made of so I suggest this as a make sure you think the ducts are sturdy enough to handle it. If it were mine I would take the grate off and run my shop vac hose down the duct to see if it sucks any thing out of it.
2014 Ram 2500 Cummins Megacab 4x4 Longhorn
2015 CrossRoads Longhorn ReZerve LTZ31SB (basically its a Zinger ReZerve 35' bunkhouse that has been decked out Texas style)