Those drain tubes cleaning brushes work great. I have used a coat hanger in the past to "push through" the dirt in the vents. Then I run peroxide through it, let that sink in and dissolve the grime for a few minutes and then I run clear water through it till it drops out off the drain openings on the underside of the car.
If water does not drain from multiple openings you know it's still clogged.
There are three drains under the windshield wiper cowl - on on each side and one in the middle near the alarm siren. Make sure all are free of debris.
There is a thread on here where someone cut a small hole into the cowl so he would be able to clear the drain periodically without having to loosen the wipers and pulling up on the cover. He then used a rubber plug or cap to cover it. There is a DIY in the forum. Pretty cool idea. Most people clean the drains once a year. Good luck.