cowl area

I pulled the dash on my 65 Barracuda and found a lot of rust on the driverside.I knew I had water leaking in as when I bought the car I had water in the floor after a hard rain. The bottom of the cowl has some rusted out areas which will have to be repaired. My question is I read there are draniage tubes in the cowl that get stopped up. Can you come from underneath and blow these out with air and if so where would these tubes exit. Are they in the engine compartment or do they exit near the bottom somewhere.
Thanks for your help.