hmmmmmm...Suppose its not really an overflow pipe, rather than another modified durso standpipe..Saw the image on the net earlier on a different site and they also described it as a Modified Standpipe....
12-14 inch length of 1 inch pipe, which ties into a 1 1/2" expansion coupler(the slide thingy)which then ties into the 1 1/2" "T", which finally ties into the 90 degree elbow at the very top. The top side of the "T" has a threaded cleanout cap, not sure its function, I only added it because I was going off of the picture of the one sold by ALL-Glass..
According to durso's site, there's suposed to be a whole drilled in that cap, to vent it. Without that vent, I don't think it will work the way it's suposed to. eg., if you were to just set it up the way it is and turn the return pump on, the water would have to compress the air in the top of the standpipe before it starts to drain.
indeed, I noticed that while reading on the site as well. This is most likely the reason that the all glass version has some kind of threaded top, they must have a way to adjust how much air is being let in by opening or closing, this is something that I could not see from the drawing on their website. thankfully the threaded cap I used has a flat top about 1/2 inch wide, I can drill a hole nicely.
Spot on there Arn..One of the parts of design of the standpipe is to drill a tiny little whole in the top of the pipe. Here is a quote from the person's site who designed the standpipe to start with...
The End-Cap is held on with teflon tape. A very small, as small as I could make it (thickness of a toothpick), hole is drilled in the top of the End-Cap fitting. This allows some air to enter into the standpipe. This size air hole worked well for my setup, you will likely need to tinker with it. I would suggest starting with a 1/16 inch drill bit for the air hole in the End-Cap. If you find the water level in the chamber fluctuates quickly then the standpipe needs to suck in more air. Try a 5/64 inch drill bit to make the hole slightly larger -- increasing the size if need be. Do not be surprised if you need to go as large as ¼ inch with the hole size. The lower the flow the larger the hole size needed.
The hole on the top of the standpipe (in the End-Cap) is very important. Without the hole, a full siphon will be created and water will be sucked out of the overflow chamber to fast. The water level will drop below the intake and you will get a terrible air sucking noise. If you drill a hole and the water level still drops to far (making a sucking noise) then the hole is to small. Just make it slightly larger (see above) and the water level will raise. If you make the hole to large then the water level will be to high. (It should not overflow the tank as it will not get that high, but keep an eye on it). If the water level is to high this can be fixed easily. Seal the hole with aquarium safe silicone and use a toothpick to make a small hole in the silicone. If this turns out to be to small, remove some silicone with a smaller drill-bit or some other tiny sharp object. No silicone handy? You can try some old well chewed bubble gum to reduce the air hole size for testing If you really mess up, then get a new End-Cap (they are cheap).
Be sure to create a screen out of lighting grid or fish and snails can get inside and cause a flood.
I have two Durso standpipes on my 180 and when one clogged up, the other saved my bacon. The main principle here is to have larger pipe at the top and smaller at the bottom for the Durso. I have 1 1/2 going down to 1 inch through the drilled hole and then to a hose to the sump.
The tiny hole at the top cuts down on the gurgling noise. I took the tops off of mine with a problem. If vent hole is not large enough or gets clogged, the water level in the overflow will rise before the siphoning begins and then swoosh, the siphon kicks in and you get a big flushing sound.