Saving as much water as possible is important but not for bacterial reasons. The fish are acclimated to it's chemistry and it makes the transition back that much less stressful to them. If you can save as much as 50% (or more) all the better. You must also ensure not to feed them the day before transport and not until a day after being placed back in the newly re-set up system. You should be sure to toss out any transport water as it will cause fouling depending on the number of animals to be transported.
If at all possible you should go a day ahead to the new location and prepare as much new SW
as possible, this can be very important. That way you will have some back up water as you will end up losing a good % with the transport. The sand can stay in the tank with an 1" or so of water to keep in moist depending on depth. You do not want too much weight in the tank or the seems will be stressed and cause possible leaking when moved. The rock can be transported in a styro box(s) with SW
soaked towels unless encrusted with corals you may need deep pails with only enough water to cover the rock. I would also suggest bagging as many animals as possible start with corals (if any) and the fish last just before leaving. Once at the new local, get the tank set up and heated ASAP
. Start floating the fish to equalize temp first thing while you are arranaging the rock. Once the temp is good open the bags and add a few drops of an ammonia detoxifier. Acclimate the fish and then begin acclimating the corals. Do not do both at the same time unless you have ample room. The corals will fair much longer than the fish. Once all is said and done, turn off the lights to help with any stress the fish may be feeling. Keep an eye on the temp and general fish behavior for problems for the next few hours.
The key to success is being properly prepared at the new location. The more you can do there, the less stressful this will be for both you and the aniamls.