An example of draining tanks
Years ago I was moving across town, running a 75g SPS tank. Was feeling lazy, so I rented 20 5g water bottles with caps. Drained tank into bottles, disconnected the plumbing and loaded the full reef with fish flopping around the bottom into a van on 4x4 blocks. Drove about 10k across town to my new condo, moved the stand in, carried tank up and placed it then dumped the water bottles back in the tank. Other than some really annoyed fish, everything was fine. Nothing moved or shifted, all corals were intact
Did it again moving out of the condo into my current house.