I do 10% water changes on my 300 gallon system, which is 30 gallons per water change.
I make up the water ahead of time in a 30 gallon rubbermaid trash can. I usually make it up to a week ahead of time, and I have a powerhead running in it to keep it circulating. Before I do the water change, I make sure the salinity and pH are spot on. I don't use a heater in the trash can, and the water is usually within 5 degrees of my tank water anyways. But for people who don't live in a climate like Arizona, it's best to have a heater as well as a powerhead running to keep the temp in the right range also.
Then I have a submersible pump hooked up to vinyl tubing that I put in the tank. The vinyl tubing goes to the sink, and I turn the pump on, and that pumps water from my tank to the sink. When I get to the correct level, I move the pump into the new water and the vinyl tubing into the tank, and that moves the new water into the tank.
For a 30 gallon water change using a pump, it takes me less than 15 minutes to do the whole thing.
Oh, and I turn off all the powerheads and the return pump before the water change too, so they don't run dry.
Moving a 55 gallon tank is easy. If you are even mildly strong, you can move it all by yourself. I can't lift my 55 gallon tank by myself and be stable, but I have an exhusband, a friend's husband, and my current fiance that have all moved my 55 gallon up and down stairs all by themselves. They just put it under one arm and moved it. Two people will be able to move it with no problem. Hell, it only took two people to carry my 240.