For my 150gal I siphon the water out with a tube through the backdoor. I then take the showerhead off, pop on a hose adapter and clamp down a clear hose, put the other end in the tank and turn on the water - work great. Of course I do have a hose holder on the tank so it doesn't come out of the tank when i turn the water on. I add a good chunk of water conditioner in before I turn the water on and while I am filling it. In total I add enough to treat the total gallonage of the tank.