I saw this on YouTube. A guy named Nestor did it so I give him all the credit. I had water on the floorboard behind my driver’s seat in my 2014 Altima. Two mechanics tried blowing out the lines with compressed air, but apparently neither one of them bothered to test whether the drains were actually clear. Speed Test
I bought a $5 bottle of two-part drain cleaner and a turkey baster. I had about 3 feet of 3/8” (?) hose that fit snugly on the tip of the turkey baster. I sucked up the first liquid and put a dose at each corner, using the tubing to get way back to the rear drain holes. I rinsed out the tubing then did the same with the second liquid. I waited about 45 minutes (directions say 1 hour) and poured a little really hot water into each track. Voila! Water drained from all four corners. Never disassembled any part of the car.