dannieboiz, I have had my tank hooked up with this:
http://www.spectrapure.com/St_alc_p2.htm for almost 4 years. It has been key to an automated system. Whatever you do, don't just use a float valve as they can fail. In addition, if you decide to go this route make sure to install this:
http://www.spectrapure.com/St_PTD_p0.htm
I don't disagree with Marc. I'm sure a lot of people have had disasters; but my experiences with using this have been very good. If power fails, it automatically shuts down the system. If the pressure vessel fails in the sump, the float valve is the backup. It would take 2 different things to fail in order to overflow the sump.
In addition, I designed my RODI system to also go to a Brute holding container. Now that has only a float valve.
For example, if I am making water and it is dripping into my Brute container and my sump gets low at the same time, the system knows to prioritize the water to my sump. As soon as the sump tops off, water will shut off to it and it will again begin dripping into my Brute container. This has worked flawlessly for me.
Hope this helps.