Troutus, all you need is an elbow with enough angle on it that water is always in your outflow pipe.
Yours is a traditional stand pipe it sounds like, not a "true" siphon setup, but the elbow on the outlet of this drawing from
Pond Dam Piping is what you want to add.
You can also change your stand pipe to a bottom draw system by merely slipping a larger and slightly longer pipe over the your current stand pipe...that will stop top water from being pulled in and draw it up from the bottom instead.
