I either use my python or a maxijet and suck out what I can out of the display/sump into five gallon buckets(only for measuring purposes) and dump them in the toilet. Then I use a mag 18 to pump new water up from my basement.
Soon mine will be totally automatic. I will just have to turn a couple ball valves and away we go. Stay tuned to Jason's 120 for details. I am trying to trade frags for equipment.
I got one 30gal can with water mixing,and one that I siphon 25gal into(got it marked).After I siphon out the old water,I stick a hose on my Rio1700 and pump the mixing can empty.Change done.