I'm not arguing with you mark, but if you watch the flow I'm betting it won't be constant. At least it isn't with my unit. It starts, tops up and then stops, 20 minutes later it starts again, drips a bit, then stops, and does this throughout the day. Maybe your tank is much larger and has more evaporation.
Here's an idea I got from RC.
The idea is that the entire container holds 4 gallons, it fills all at one time. The left side has an airline that has a check valve so as it fills it forces the air out, but the check valve prevents air from entering so a vacuum is created and the water level will hold up as the float valve is lifted & the water will turn off. At that point the entire container will be full. The right side will slowly lower as the water goes to the sump on the basis of the float switch in the sump. But the left side will remain topped up so the RO unit will stay off. When the right side gets low enough it will break the siphon and the left side will empty, the RO unit will turn on and start to refill the entire container. The siphon break probably won't empty the entire left side but hopefully most of it will drop from the sheer weight of the water.
The advantages of this design (again, it's not my design) are as follows:
- it doesn't rely on any electrical devices that can break down
- it uses your RO unit all at one time for 4 gallons of water
- TDS creep won't be much of a factor
- your tank gets evaporated water replenished immediately throughout the day
It could be supplemented with another float switch on the right side that connects to a solenoid that is inline on the RO line. If the water level rises too much to trip this float switch (i.e. if the left side malfunctions and the water level keeps rising) this solenoid will shut off, otherwise it will always be open.