Does anyone have any experience in dealing with forced air floor ventilation? Our system is failing due to old piping rotting and filling up floor vents with sand. The runs are 200 to 250 feet long 90 in total tried running a camera up a few holes to see what's going on but pretty sure its sand. Can only get in about 70 feet before the camera cable starts to just buckle on it self. The holes are about 8 inched in Dia steel corrugated pipe age is about 40 years old looking for a fix with out having to empty the rooms and removing the racking to tackle the job from the top.