Thanks Mandarin! Yeah, we can rip out some sort of tunes or another :lol:
So, I'm not sure what you mean by sidewall mounted surge. Does that just refer to the surge bulkhead exiting through the side? If that's it then yes we are describing essentially the same thing. You are correct about the key being getting over the hump.
I chose to go though the bottom because of the curved walls of my surge tank, to make the height of the U completely adjustable, and to reduce the footprint (pipe goes straight out the bottom and into the display tank) Your plumbing will do the exact same thing, but with less of it actually in your surge tank displacing water.
As far as height of surge tank above display tank goes, I think you should be OK with your surge a few inches above your display. 20 gallons at any height should provide a lot of pressure. I at first had my surge tank resting right on top of my display tank and got an adequate surge. It is now sitting about where it is going to end up- about 8 inches above the water. This gave me a little more powerful of a surge, but I had to adjust the air vent all over again for the new height. More height= faster surge + more pipe that has to fill with air to break syphon. I'm guessing that less bubbles will be produced and adjustment will be easier with a larger, shallower surge tank that is not very high above the tank.
For the air vent I had originally drilled a small hole near the intake of the surge pipe, but I ended up cutting and drilling every spare piece of 1.5" PVC I had trying to adjust the size and height of the air hole. I now have an extra 1.5" PVC Tee instead of that hole. The Tee has a short piece of 1.5" pipe that sticks off to the side that is capped. I drilled a small hole through the side of the cap and pipe, and then twisted the cap on the pipe for adjustment. I can also turn the cap AND the pipe together to adjust how high the hole is. You can probably accomplish the same thing any number of ways- the airline tubing sounds pretty good. You will want to be able to adjust the size and the height of the hole.
The only problem I can see with that big of a surge is that your main tank overflows have to be able to handle it. You don't have to drain the entire surge tank though, maybe make the tank into a 'fuge with the top several inches surging. I added a small light to the top of my surge bucket, and now It is just COVERED with coralline algae, limpets, snails and coralline eating starfish. What's your plan?