Gaining Access to the Wiper Drains

There's gotta be someone on this board that knows HOW you gain access to the inside of the wiper drains. As I've explained it prior posts, I've removed the cowl and traced my interior leak to the DRIVERS SIDE drain hole. Water enters the drain, but never exits the vehicle. Hence my wet drivers side floorboard.
Someone PLEASE explain to me HOW you get into the part of the body where this drain path is.
I'm going crazy with this!