previous discussion
http://reefcentral.com/forums/showthread.php?t=2269426&highlight=balancing+pipes
assuming bean setup
"Inverted siphon" is plumbing that pushes water up into the final sump AKA reverse siphon.
1.5" emergency that expands to 3" pipe and meets the durso pipe. The higher you place the junction the better as the inverted siphon will require pressure to fill the downline sump. You don't want the water level above the first junction to avoid stagnant water in the emergency line, the water woun't be stagnant after the durso line. the junction of the siphon line needs to be below the water line in the durso/emergency line for the siphon to work (conservatively). I would use 45 degree T's in the 3" diameter pipe with 45 elbows on the durso and siphon lines.
the disadvantage in this setup over a two sump is no trap for snails, fish or detrius that get sucked down, hopefully the bean has a good screen anyway for the livestock but the detrius will continue to build up in the horizontal run and will need a flush to prevent high phosphates. A T and a ball valve directly into the maintenance drain would be a great option you could do all the water changes that way.
A two sump setup would be advisiable if there is room. just like a standard sump but with a gravity overflow with ~9" of height to spare flow and friction loss dependent. that will leave plenty of space for the inverted siphon and give you a great area to remove particulates.
Cleanouts will need to be planned according to the setup however they present leak risks, pitch would be great but you are limited in height difference by the slab and would not want to go down more than a few inches to avoid slab damage. If was planning a cleanout I'd use a sump (like a bucket below the waterflow) to capture most of the detrius in one location and just pump that out.
worse option is balanced pumps but that has other major issues.
I thought about doing this at my last home but ended up going with a smaller fuge, limited livestock, and GFO to keep phosphates down. You can still fit a lot of stuff under a 180G, just plumbing a drain alone would give you many benefits without the hassle and risk with a remote sump.
Also don't try and go under supporting walls!!!