Questions on DIY auto top off system

hmmmm... By ATO do you mean just a float valve hooked to your sump from your RO? That is what i have and it works great! you need to make sure you get an Auto Shut Off Valve though for your RO so it doesnt constantly make RO water... When the float valve opens RO water goes in, when its full the float valve shuts off. The back pressure puts pressure on the ASOV and the ASOV shuts off the Water (im no plumber but it works something like that from what i have been told) I even put a "T" in the line and went to a garbage can with it and have a float valve on that for my new salt water make up for water changes.... And then another "T" with a float valve to a water pitcher container so that i can fill up containers for RODI water for mixing my Two Part solutions... IDK if this is what you meant by an ATO system, but that is what i have and it works! If i had to do it again though i would use float sensors and get the BRS 50ml dosing pump and go from one container with a float valve to my sump, and then another one to my trash can, because sometimes float valves are a little dangerous, if something pushes up against it and keeps it on... you may have a flood... But i have sensors on my sump so when the sump level is too high (almost to the top) it will shoot me an e-mail and a text...