Look under the car at a point where the outer shell of the rocker panel joins the the floor pan.

There is a seam that runs the length under the car. It will have puckers every foot or so.

Most of the water that goes down the cowl vent should drain from the front area where the rear of the fenders attach on the bottom.
If they plug up everything floats in there!

Those plastic plugs pop out all, along the inside of the car to give you access to the debris inside. There will be plenty and sometimes as far back as the rear door pillar.

The same goes for the door panels as there are two of them along the inside shell of the door.

Phil