After doing some research I think I'm gonna go with the dual float valve + solenoid solution. My plan is to run the solenoid for an hour a day, once in the AM and once at night. That way I'll be home if there's problems. It would also allow the ro/di unit to run a while and not just trickle all day. I'm still a little clueless as to how it all goes together. I assume that the good water line off the ro/di unit goes to the solenoid which in turn goes to the float valve(s). The waste water will go through the wall outside. If I get an auto shut off valve on the ro/di unit it would prevent it from running waste water all the time, correct? In other words, I don't want it pushing waste water through when the ATO is preventing the flow of good water.

Sorry for all the questions! I'm still a novice when it comes to reefing and a complete noob with the ATO stuff. Thanks for the help and suggestions though!