The u tube I had I had to drill a hole and put an air fitting in it. I don't know if they come with air connection or not. You could try putting the tube up inside the u tube at the upper most point and leaving it there but not sure on that.
I thought I could do that as well but wasn't totally sure that would work. If I put the fitting in the U tube it would have to be on the very top at the curve right?
If properly set up and maintained, you shouldn't need a pump to hold the siphon. What model overflow is it? The ones with U-Tubes especially don't need them.