[Horace]

For those reading you need to avoid syphon both directions. You need to pump OUT to a point higher than the topoff container ( I use a RO Solenoid with multiple safety float switches instead), and you must not have the exit of the topoff water hose under water or it will create a back syphon. I personally like low maintenance, so I prefer the slightly more dangerous method of hooking to my RO unit and using switches and failsafes instead.