I use Saran Wrap to plug off both sides of the over flow tube while under water, then put the tube on the overflow box and then remove the Saran Wrap. Most of the time all the air is out if I made sure the air was out before putting the Saran Wrap on. Also ensure there is enough flow on your drain piping to your sump.
I then adjust my return pump to keep the level right in the sump. I always have to keep an eye on the sump level as it does go out of adjustment based on the noise reduction foam tube covers and roller-mat fleece filling up with debris and as the display level fluctuates from evaporation. I am always changing the return pump flow to stay in balance.
I do have an ATO level float switch in the sump but I have to be careful with it as it will come on based on low sump level. Especially, if air gets in the overflow tubes and or I lose prime on one overflow pipe. I have my sump level monitored by my Apex and my ATO programmed to shutoff below a certain level as not to add too much RODI dropping my salinity.
Occasionally, one overflow tube loses its prime or air gets in it. So I have to redo the priming and then open up the drain piping gate valve to allow more flow.
Wish I could have drilled my tank instead of using the hang on the back overflow. Tank appears to be tempered glass on all panels so I could not drill it. I spent all the money on equipment but cheap’d out on the tank. Looking back I should have ponied up for a higher quality tank then drilled it. Hang on the back works but takes more monitoring and adjustments than what I was going for as I travel for work sometimes.
