· ATO COMPLETE gravity system with 10 gal can, tubing, float valve, and cabinet $60 A very simple and elegant solution with no electronics. Just a water can placed on a cabinet above sump level to facilitate gravity drainage. How the ATO works: 1. RO tube is connected to float valve on top of the 10gal trash can. Once the can is full, the float valve will close and stop flow. You can see an attached manual stop valve on my blue RO tube which I use when connecting and d