They must be some very tight curves if your tygon wont handle it.
It might be worth looking at some gradual bends as you mentioned, the best example i can find at the moment is some eheim ones here
http://www.silverprop.com/sp/shop.asp
either using sleeve bends, or elbows that are'nt on a straight 90 degree bend. Either that, or im sure your local plumbing/hardware store will have something similar which should help the water flow smoother.
Edit: should also mention, if you can't find 'Y' fittings with a nice wide internal diameter, i've seen sections cut off a thick sheet of perspex/acrylic used, drilled out at the top from angles into a vertical inlet, just drilled and tapped with BSP hose barbs epoxied in. Difficult to explain, but the general idea is there.