Originally Posted by
Kynekke
Option #2... fill the tube with water and seal both ends with saran wrap, holding it shut with your hands. Turn the tube over, holding tightly so the saran wrap holds in the water. Once the U Tube is seated in the overflow, pull both ends of the saran wrap off, pulling the sump side .000001 second faster than the tank side. The suction starts automatically that way.
I was pleasantly surprised to note that you only have to do that once... even shutting down the sump return during a water change didn't break enough of the suction and when you turn the water pump back on, the overflow suction starts up again on it's own.
That's how I use to do it....