I need help with this noise the overflow box is making.
http://youtu.be/FyY7lP8CSQs
http://youtu.be/FyY7lP8CSQs
The airline tubing is acting as a siphon break by letting air into the pipe. It also keeps it quieter. However the pipe isn't getting enough air for the amount of water it's draining so it keeps siphoning even though it has a siphon break. You can either slow down the return pump to slow down the amount of water through the overflow box and then drain pipe or you can increase the size of the airline tubing. You can increase it to 3/8" or 1/2" RO or airline tubing and put a valve on it. Although you aren't running a full siphon system at all like a Bean Animal or Herbie so I am not even sure a valve on the airline will be needed. Bottom line is that if you want it to stop siphoning you need to get more air in the system by increasing the size of the tubing.
Its possible that tubing is clogged, that's why I suggested to remove that tubing first. But no response on this thread yet...