I will start out with my 65 Hex, the last tank I set up for automatic water change. This system went together very quickly, I think the whole thing took a couple hours at most. I have well water, so no prefiltration is used.
The first thing I did was set up the float valve. This valve (Eshopps) is fairly cheap ($29.99 @petsolutions) and is a very cool idea, but it has some serious flaws in the construction of the bracket. I have been looking for a better alternative, but I haven't found it yet.
The bracket clamps onto the side of the tank and holds the float valve in place. It is designed to let you set the water level between about two to three inches below the top of the tank - this is the first problem, in order to keep the water level in the tank full, I had to drill an extra hole in the bracket to allow me to mount it higher. No big deal, but annoying.. The second problem is that while the bracket looks quite sturdy (it is made of .25" acrylic) the glue joints are horrible. It is as if they assembled them with contact cement rather than acrylic solvent-weld. This is also annoying but fairly easy to fix by popping the pieces apart and regluing them with proper acrylic cement.
Once the valve was mounted at the right height I attached the included 1/4" supply line to a valve that I teed off of the cold side of my hot water heater.
The water removal is performed by an Aqualift pump. The inlet side is adapted from 1/4" O.D. (airline size) tubing to a piece of 1/2" I.D. black vinyl tubing, a 1/2" barbed elbow and another piece of 1/2" tubing pointing down into the water (sorry that the photos aren't clearer)bing is packed with filter floss as a prefilter to protect the Aqualift.
The exit side of the Aqualift goes into a 1/2" tee fitting - the downward pointing part goes to the drain, the upward pointing part loops back into the tank (but not into the water). This serves as a syphon break, so that the drain can't continue to syphon when the pump shuts off. The half inch drain line connects to another drain (from my 75) and then goes through a hole I drilled in the foundation. It is connected to the house drains/septic system.
This is all you see of the float valve from inside the tank:
This is the view of the Aqualift inlet tube: