cowl drains

I've used a air compressor with a blow gun to loosen the clumps by blowing from side to side and through the cowl grill then opened both inside vents and vacume them out and repeat. Also make sure you vacume the heater core out too. Is the blockage wet or dry? If wet just hit it with the blow gun to break it up so it can dry out. If you have no carpet and don't mind the mess just leave both vents open as you blow them out.