I take the water from the plumbing system under the tank.
I use two buckets. One is filled with fresh water and one is empty.
I have a spare submersible pump which I attach green Eheim hose to and place in the bucket of fresh water. This is connected to the water-in ball valve.
A hose is attached to the water-out ball valve which leads to the empty bucket.
I turn on the pump and open the ball valves. Slight adjustments are made to the ball valves as it drains faster than it pumps in.
When I'm done, I shut the ball valves, turn off the pump and disconnect the hoses. I use a small towel to grip the connectors with to soak up the drips before I pull the hose away.
The waste water gets poured onto the garden. Only the green bushy plants though, rather than fruit or flowering plants, as high nitrogen levels will hinder the fruiting/flowering and cause more green growth (according to Mother, anyway. Lol).
I don't think it could be any easier in my particular setup. The tank doesn't get disturbed. Plants stay where they are. Fish don't know any different.