Just a little helper. I measure the distance from the top of each tank the 1st time I do changes, then put a little piece of tape at that spot when doing future changes and I never have to measure again. I use a big diameter hose and siphon into the tub, sometimes using a vac. I keep make-up water mixing in a big garbage can on wheels; the mixing pump has a piece of hose attached and I just wheel it out and fill the tanks. I'm working on a real neat, almost work-free system...but it still needs work!