Did you cut the upper part of the emergency elbow down? I think you want that about 1" or so below the level that would fill up the tank, but with that said, I think it's probably fine with it where you have it shown, but if for some reason you had the siphon and OC clog up and you were running just on the emergency, the water level would probably be above the inside bottom or the euro. Cutting off the upper part of the elbow (the flange for solvent welding to another piece of pipe) would eliminate that risk.
Nice to see a thread for this setup! On the other site, it's spread out across a few threads