I'm not a very big fan of the drip method with nanos. It takes too much futzing about with the rate and of course as the bottle gets lower the flow rate decreases.
What I did for my was order some float switches from floatswitches.net. I took a battery operated pump, opened it up and clipped one of the wires going to the motor. I then simply spliced in the float switch, one lead to each of the clipped ends. Close the pump back up. I then took a piece of acrylic and heated it and bent it to an L, drilled an appropriately sized hole and mounted the switch. To mount the bracket I used high strength velcro. I placed a strip on the outside of my tank and a strip on the bracket. This allows me to adjsut the level that I want the water to come to. Then take a pop bottle or some other sealable containter. Drill two holes in the top. Cut a short piece (about 1-2") of rigid airline and insert it in one of the holes and glue with crazy glue (AKA cyanoacrylite). This will be the tube that your air comes in through. Cut another piece of rigid airline that will reach the bottom of the container and sitck out about 1" above the lid. Place this in the second hole and glue with crazy glue. Run airline from the short tube to your air pump. Run airline fromt he long tube back to your tank. I suggest using rigid tube at the tank. You can heat it gently and bend it to hook over the edge of the tank. Make sure that it does not extend below the water surface or you could end up with a back siphon problem when the topoff turns off. Fill your bottle with distilled or R/O water. That's it! I chose to use a battery powered pump because it only uses 3 volts DC. Most of the available switches out there are rated for DC, not for AC. This reduces fire risk, switch failure risk (due to high power loads) and of course the all time favorite risk of electricution.
I've been using this system on both my 4 gallon and my 1 gallon for several months and it works great. Just remember that if you have the flowat switch in an area with snails then you should definitely put a snail gaurd on the switch. Just get a pill bottle, drill small holes in it to allow the water to enter, drill an appropriate sized hole in the lid so that the switch post can go through and you're done.
I hope this helps. I'll see what I can do about posting some pics later.
