Drain hole cleaning methods?

I also had a bad passenger side leak. Turned out it was not coming from inside the cowl area, but water, doing what water will do, was coming in somehow from the area under the hood where all the pieces of sheet metal make a sandwich. I think through surface tension, it was going down, and then back up under the ledge where a lot of people mount the electronic ignition module. I ended up sealing up under that lip, and the leak went away.