I think many siphons use a Y with a clean out port where the suction pipe goes into the water. How about putting the clean out port at the desired high water level so in winter you just leave it open like a traditional overflow pipe then plug it back up at ice out. It won't have the capacity of an active siphon when in "winter mode" and this should be considered during design.



"The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge." Stephen W. Hawking