Are you asking about my setup or are you asking about the possibility of water going from the overflow back into the tank? My setup has a sump in the bottom of the stand. I can send pictures of that if you want. If you asking about the water going into the overflow and then back into tank after some sort of filter, then that changes the overflow into a typical hang on back (HOB) filter. I made the overflow to get the water to the sump for purification and then back into the tank. Let me know if this helps. Cheers.