Ok I ended up changing the size of my reserve tank to a 37 gallon Brute trash can. It will hold my RO water for the Tunze Osmolator top off and also for a storage for water changes. I will just drain out the water I need to a mixing bucket when I do the water changes. (sure beats waiting for a bucket at a time :blink )

The question is for all you OSMOLATOR users: Do you use a holding container larger than what your sump can handle? I'm worried if the Osmolator ever fails it might keep pumping and overfill the sump. I've researched on RC that it hardly ever fails but would like to know if anyone has experienced a failure here. I might put a milkcrate or two inside the trash can to move the Osmolator pump higher so it would turn off before it would overfill the sump. That should leave me plenty of water below the pump run dry line to still use for a water change.