ill try and get some plans together when i get time but i cant see the overflow failing because it will be 1 that keeps syphon even when the power goes out
YouTube - ‪Nano Lagoon (DIY Overflow)‬‏
this isnt me but its what i plan on building.
it will only work when the water is above the overflow level. so if the power goes out the canister filter will stop and the water will only overflow untill it goes below the intake pipe.
Another advantage i thought of is that with the canister filter having a mechanism in it which makes it easy to remove the input and output tubes without loosing all the water out of it ( kind of like the fluval 205,305,405) then it will prevent a back syphon if the power does decide to stop.
again ill try n get pics n plans up n see what you all think. thanks for the comments tho.