Next, you will need to add a float valve to add to your barrel, while this isn’t 100% necessary it will save you from having to think about the water being left on. Which you can find Here
Next on your list should be an auto shut off valve like This Without this valve, none of this setup will work so this is a must, What I should also mention here is this device fits on to your RO waste water and good clean water ..the top will say IN and OUT .. This is where your good water goes into the In Part of the valve, the part on the other side connects to your float valve.
1.Good water In
2.Good water out
On the backside of this device you put in your wastewater in and waste water out.