How do you grease your trailer bearings?

Here's a question for those in the know...

When you put grease in your trailer wheels for the bearings, how much do you add and how do you know when to stop?

As I understand it the grease is there to not only lubricate the bearings, but to keep water out of the bearings when you dunk the trailer.

I also understand that if you overfill the bearings with grease, it can pop the seal and grease will get into your trailer brakes requiring a total rebuild of your brakes.

What's the proper technique?

Thanks