I went out and spent ~$70 on tubing (1", I think), filter caps and T-fittings. Then I put tubing into each of my 3 tanks, connected them together and through a piece of tubing with a screw-on fitting. Each tank has a valve on it.
When I need to do a water change, I put the loose end of the tubing out the window, open the valve for a tank, drain it, close that valve, then repeat for the other two. When it's time to refill, I've got a powerhead (can't remember what it is) with a flow rate of ~250Gph (I think).
I attach the loose end of the tubing to it, drop it in a garbage can of water, then turn it on. As the tanks fill, I turn off each of their valves. When all the tanks are full, I turn off the powerhead and toss the extra water in my garbage can on my lawn. Easy peasy.