Depending on the size of the tank, distance moved, etc and what you want to do, i.e. add 100% new water, etc. there have been several good suggestions. If you wish to not disturb the sand, then drain the water into several 15 to 20 or so gallon containers (rubbermaid?) (anything larger becomes very heavy and bulky).
Put your rocks, etc into this water. You don't have to "bag" the fish, either. Just put them in there, too. If using rubbermaid containers, be sure and use the lids. This keeps water from sloshing out and gives a little better rigidity/strength to the container. For short moves, you don't need to worry about lighting, temperatures (too much) or water circulation.
Drain the water down to just above the sand depth. If possible, move the tank and stand as one. I would only try this if there is a lip or some way around the stand edge to keep the tank from slipping (as in my 45 hex). This will help keep it from torqueing. But this is/can be very heavy and bulky and you need plenty of help. If done this way, be careful about having a high center of gravity (tipping) during moving/turning. This is the way I have moved my 45 gallon hex. I have not moved anything bigger/longer such as a 55, etc, so doing something that large may not be easy/doable this way. My hex's stand does have a lip around it, so the tank could not slide around and off. Me and my daughter were able to carry it short distances, but it was difficult.
If it is too big, heavy and bulky and not reasonable to move it like this on the stand, then I think I would drain it all of the way and remove the sand. I don't know if I would add this sand back since I do not know what/how much bacteria, detritus, etc would be released. How much that would impact it being set up again, I don't know. I have moved my hex 4 times like described above and have never lost any fish. The shortest move was just a couple of blocks and the longest was about 50 miles (twice). Once, it was done at night in the middle of December so I had a pretty sizable temperature drop, but they all made it.
I don't envy anyone who has to do any kind of a move. I know a lot of movers, carpet cleaners, etc will not touch an aquarium. Best of luck to you folks that have to do this.
Frank
