How do I get the Water out that is sitting in backup lights in 2005 Chevy Impala?

i have the same car an problem, an what i did was take that whole assymbly off and drained it, To do this, open up the trunk and behind the light panel will be cut outs in the metal that allow access to about 12 nuts, take those off and pull the light panel away from the trunklid (it will have wires still attaching it for the lights) Grab the light bulb assymbly and twist and pull it off. Now with it off the car turn it flat and slosh it around(took a couple minutes to get it all out) Dont know what causes this , but i took silicone andcaulked every gap i found (upper left and right corners, and hole where the lock cylinder protrudes through the assymbly). Not sure if this fix works since i just did the other day. Goodluck, hope i helped