Does the overflow have a hole in the top with an air hose coming out?
It does not look like the siphon tubes do.
But to keep from losing your siphon... you can shove air hose into each tube until the end of the air hose is at the very top of the siphon tube.
Then attach the other end to a power head(s) or a small pump made for pumping water. ( The pumps cost about about 9 bucks... and I have one on my overflow.) Sure makes starting the siphon easy!
Also.. for the return line.. I have mine going to almost the very bottom of my tank.
At first... when I cut the power to the return pump, a siphon would start(and if I had not been there to turn the power back on.. I would have had 110 gallons of water on the floor.)
So...to prevent a siphon from forming in my return line, I drilled a hole in the return line just below the water line of the aquarium.
Now if the power goes out.. a siphon starts and the water from the tank begins to empty into my sump tank.... BUT when the water level drops below the hole I drilled, air enters the return line and the siphon is killed.
I hope this makes some sort of sense!