I had to make some minor modifications to the overflow system to get it to work exactly as designed. Mainly, when I shut the ball valve on the main siphon line (to simulate a clog) the two emergency drains couldn't handle the flow fast enough and the return section of my sump ran dry. Really, I should have just designed my sump with a bigger return section, but here is how I fixed the problem:
Cut down the emergency drain:
This allowed water to start flowing through the emergency sooner and gave the open channel some extra time to purge all of its air and start acting like a siphon. Also, in the same picture you can see that I zip tied the open channel's air line as close to the overflow box's water level as possible. This allowed the open channel to start purging air and forming a siphon the moment the water level fluctuates at all.
Second, I cut some anti siphon holes halfway down the siphon pipe's intake.
This breaks the siphon early when i turn the return flow off and stops the overflow from draining those extra two inches of water below it into my sump. This allowed me to add more water into the sump during the "turned off state" so that my return section would be higher during the "turned on state".
Along the same lines, incorporating good anti-siphon holes in my return line lowers the amount of water that falls back to my sump when the return pump is off, allowing me to add more water to the sump to reach my maximum height.
As it is now, when I simulate a blockage of the siphon pipe the water in my sump drops down to about one inch above my return strainer before it goes back to its normal operating level when the open channel's siphon finally kicks in.
