A small hole in the top of the bend will break the siphon won't it?
Yes thats a better way I reckon. Done that with 4" bends into/out of a home made septic tank using 3x IBC's but didnt think of it for an overflow. Wonder if it complies with bylaw 49 ?

I read that you've bonded all the metalwork together, which I think is a good idea. Have you attached an anode to the bond? (zinc, magnesium block etc) Or are you going to impress a voltage on a sacrificial piece of copper or somesuch?
Brandon pointed the way to zinc anodes for boats and I have a kilo of it hanging off the crossbonding wires approx 0.5m down.
Pontiffs link advised against impressing a voltage, as it could create pitting, whilst giving general protection (IIRC) -
http://www.authorstream.com/Presentation/Cubemiddle-36438-UN1001-Galvanic-Corrosion-REACTOR-CHEMISTRY-Section-4-Eight-Forms-SERI-as-Entertainment-ppt-powerpoint/Aint Navitron Brilliant
