all ya need are two air line hoses, and two buckets and a step stool.
you put the bucket that the fish is in on the stool, run one of the hoses from the tank you're going to put the fish in, to the bucket. then run the second air line out of the bucket to a bucket on the floor (or outside if the hose is long enough). start the syphon on the hose to the bucket, then start the syphon on the lower hose. all things being equal it SHOULD add and subract the same amount of water, but it never happens that way. you need to watch it and start or stop the syphon as needed.
keep the bubbler on the bucket with the fish while you're doing it though, and if you're doing it with an olympic jumping fish like an arowana, or peacock bass you might want to put a piece of egg crate on top of the bucket with the fish in it and weigh it down with a rock.
