2005 Pontiac Grand Prix Water Leaking through my Dome Light

I have a 2005 Grand Prix. It has been raining quite heavily lately. Today, when I applied my brakes at a stop sign, water came pouring through my dome light. I called the dealer and they wanted a lot of money to what appears to be a necessary cleaning of the sunroof drain tubes. How can I locate these tubes? Where specifically do they exit my car from? Given my research, it seems all the dealer would do is use some compressed air, on a low level, to clean out the tube (the dealer confirmed this). My question is what do these drains look like? Where can I find them? Where do they lead to? Thank you for any assistance.