There isn't really such a thing as too large of a fish tank, as far as the fish are concerned. As other people have mentioned, fish come from massive bodies of water in the wild. For very large tanks or systems of tanks or even for fish rooms, people often have it plumbed so that the aquarium can have automatic draining and top offs based on piping, drains, gravity, and some parts. For example you can have enormous containers of water attached to tanks by PVC piping with solenoid-controlled electric valves to control how often the fresh water from massive containers flows into the tank, you can set it to happen multiple times a day for fresh water in without your having to lift a finger. To get water out, you can attach a bulkhead fitting to the tank that will automatically remove water once it reaches a certain height in the tank, the old water can then go down via gravity to a drain in the floor and then the containers of fresh water will be triggered to fill the tank up again. That simple system is used in many fish rooms so that even if you have hundreds of gallons water is being consistently changed out so to keep water quality high. Many wholesale fish providers have setups like that which work for hundreds or even thousands of gallons. That's a pretty standard way to do water changes in large tanks. I know Goliath Farms (they sell livebearers and Rainbows) has a different method where they have a giant greenhouse full of variously sized vats with the water piped to overflow into an enormous mangrove area to purify it before being routed back to the tanks. Obviously they aren't manually removing the water in such large systems, but they are taking the old water out and getting fresh water in nevertheless.