I use two large trash cans on wheels (after having rinsed them throughly) and a pond pump and siphon. One can is for my new water that I pre mix. The other is for the water that I siphon off of the tank. I use the pond pump to pump the new water into my tank. I always use the same can for each process; I don't swap them around. The head is over 6 feet to the top of my tank so I need a really strong pump. Also, I don't want to have to stand there all day while water dribbles into my tank. You can also use the pump to drain the "bad" water down a sink drain. Been using this method for over 7 years.