[Flatrater]

What ever you do don't plug the hole in your muffler. It is susposed to be in their as a drain for the water coming out. Without the hole the water will fill up.

You will see at least 2 drain holes in your muffler one on each side of your muffler right below the pipe that comes in.

The water is a normal by-product of your cat. When the cat converts the harmful gasses coming out of your engine it converts the gases into harmless gasses and water.