I have confused myself and forgotten that the emergency drain is plumbed over the other two because of the cabinet lumber. The box setup is correct. This morning, it had started to gurgle again and the box was not full of water. When I pull out the secondary drain and put it back in, the water fills up in the box and stops gurgling. It could be that one needs to be glued in. I have bought a gate valve for the secondary at Lowes that might be a solution. It has always had what I thought was a lot of water coming down. Is it supposed to be a trickle?
The top is the secondary, middle is main, and bottom is emergency.
Left is emergency, middle is secondary, and right is main.