I have a lot of flood experience......
Personally, I've never been able to move the tank to get under it. I suppose that little problem will be there when we finally take the tank down.
Just be sure you have good aeration in there while the water is low. I wouldn't actually be dumping in that much new water all at once. It's quite hard on things.
Hopefully someone local to you can help you out a bit, it helps to have someone around just to commiserate with you a bit.....(right Alan?)