Any type of overflow will fail if it is to block.
Reef....If you have an airhole anywhere above the waterline of the DURSO, you WILL get NOISE and a half siphon.
The air mixing in from the drill hole will cause air injection. This will be noisy even if the hole is 1mm or 0.5mm.
My hole will let air out, but not in, so it pushes whilst initially starting the siphon and as the siphon starts, it gradually over about 20 seconds turns into a solid full siphon, the air movement changes direction and my valve shuts. The valve is designed for ozone systems, so is very rugged and reliable.
Will require maintenance occassionally.
The only time it will ever be an issue, is if a power cut turns the system off and when it fires up, my valve fails.
But that has just the same chance as a snail going in the pipe.
Luckily if a snail swims near my 32mm intake he will be too small to do any thing and more than likely end up in sump with a headache.
I have done my homework on this and it is as safe as any other system.
It is the only way of getting 100% silence as far as I can see. You are all welcome to inspect!
Lets just hope none of ours block.
8)