Craig,
Your right about the drain pipe, however the vent pipe should be empty.
If the drain pipe is an 8" pipe, with the inlet going into the pond well below freeze line, and enough cover over the rest of it, it won't freeze.
If the vent tube came out of the top of the 8" pipe at the highest point it puts the vent pipe at least 8" above water level, the diameter of the drain pipe. If intake end of vent is sat at same height of 8" above water level, all of the vent pipe is at least 8" above normal water level, thus empty, except during rain events.
