Use an inline pump. I use an expensive one with a brushless motor and drain the my tanks fast via a hole through the fish room wall to the out of doors. For someone with few tanks I would recommend one of the larger Mag Drive pumps. I have a mag drive 5 pump for the 125 at my shop. It's pretty fast and lasts a very long time. I've had mine for like 12 years. I also have a smaller one for when I need to set up QT in the kitchen. My QT tank is only 30 gallons so it doesn't take long to drain and refill from it's dedicated water storage container. It will last forever because I so rarely buy new Discus.