[Delphinus]

You could, but having done this myself and finding out what the real pros&cons are ... you don't really save that much, a clear U-tube is only about $10, and with that you're a bit better off anyways because you get the continuously curving 180-degree turn (instead of 2 90-deg or 4-45 deg bends) and also you're able to see inside to check for any air bubbles accumulating. Even if you have a venturi input which should theoretically pull out any of that air, for myself I still feel better knowing I can take a peek and know for sure that the siphon isn't about to break.

OTOH, I wonder how hard it would be to bend an acrylic tube and make your own U-tube that way.