What would happen if you run the airline you suck through down to your return pump inlet with a venturi?
How do you set the water level with your setup? Is there a box on the back of the tank that the intake runs into?
This is an epic solution!
never thought about this..
What is a venturi?
in short, on some powerheads, you notice how u can attach an airline hose to the top of the outlet and have it blow bubbles out?
connect that to your vacumn syphon instead...
Then power head turns on, the air inside the syphon will be pulled because of the venturi and you will get your autoprime...
once all the air is pulled, it will just pull water from there.
You can put in a small ball valve to close it once the air is pulled and u see no more air being pushed out by powerhead.
In short.. power head forces water in -> direction.
Current of water causes vacumn inside that tube which draws air.
If that tube is tied to your syphon, it will draw the air inside syphon.
Once syphon is air free, the power head has no more air to draw from that line and will draw water from syphon.
Close off syphon port, or you will get dirty water being pulled from overflow and spat out though powerhead.