Black water tank not draining completely

Ended up taking the TT in to the dealer a couple of weeks ago for evaluation of the black tank issue. Hadn't heard anything from them, so I went by there this past Saturday to see if they had gotten around to checking it out. I talked to the shop manager and he said they couldn't find any kind of clog, so they had removed the underbelly to take a look at the tank. What they discovered is that the tank is sagging in the middle. He actually walked me back in the shop to show me the situation. Sure enough it looks like the tank was drooping down about 3 inches from where it should be to allow it to drain correctly. He said they had already talked to Forest River warranty about it. They are going to try to put a brace across the frame and against the bottom of the tank to bring it up to where it should be. If that won't work, they are going to replace the tank. I'll post again once it's all said and done with the final result.