Fresh Water Tank
Take it back to the dealer and complain. I had the same problem. The factory approved the replacement of the tank with a different style one which has a drain valve on the bottom. A steel cross support bar was also installed to help support the tank in the middle so it will not sag.
2011 Cheveolet 2500HD 4x4
Intergtated Brake Controller
ARE Camper Shell
Days Camped/2011/37 4200 Miles Towing