IME the only way to have a surge that's quiet, reliable, and bubble-free is to have it rely on some sort of expensive actuator (linear actuator, electronic ball valve, etc.) All of the siphon/air pressure/flapper valve designs I've ever seen introduce some other problem. Plus the surge still creates the drain issue. Systems with full siphons aren't always that tolerant of sudden changes in flow rate or volume between the sump and DT. Even with a system that has redundancy, it makes me nervous from a long term reliability perspective in terms of the potential to do things like trap air bubbles in the drain, flush livestock into the overflow, etc.
I agree with the others that the best way to do this is in-tank, with modifications to your current powerheads or adding another one that only comes on when you want to disturb things. I went through this same thought process when I designed my system and it was part of what lead me to choose the VFD closed loop, but I honestly haven't programmed it to respond like this yet.
