My overflow drain has gas

[Richer]

Have you tried increasing the amount of air that gets into your standpipe? (ie. increase the size of the air hole). I found that when I was pushing lots of flow through a standpipe I'd also get the flushing effect you see in youre pictures... after I increased the amount of air that went through the pipe, the flushing stopped altogether, and the level in my overflow rarely ever moves up or down.

*edit*
Looks like Tony get there before I did

-Rich

[outtafocus]

I have a long length of the air line tubing which came with my mj1200 (the cool black stuff). The air line drops inside the standpipe to about an inch or two below the water inlet holes.
I tried to run it with no tubing and it was horribly loud, constant air sucking sound. Then I tried just a 1" piece of tubing, and it was quieter but the water level jumped like a pogo stick.
I guess I could drill out the hole and glue in a long piece of rigid pipe, but that could be loud to.

[Richer]

What I did was used my smallest drill bit and drilled a hole on top of the standpipe and slowly increased the hole size until the water level in my overflow was constant.
There are quite a few ways of getting air into the standpipe... some more fancier than others.

-Rich

[outtafocus]

I will have to go pick up a new pvc end cap and try out your method. When you finally found the right size, how was the noise?

In taking my stand pipe in and out of my overflow I managed to knock off one of my eggcrate anti-snail fences. Well I guess all experimenting must stop till the silicone cures fully.

[Richer]

There was little noise after I found the right noise. You'll know once you get the sweet spot.

-Rich

[BT05]

I don't use airline tubing either and it sounds kind of like a faint whistle.

I'm not sure about this, but from the pictures, it looks like your standpipe is half the height of your overflow box? I'm not sure this has the height to draw enough air being that far down, but it should really be about the height of the overflow. Also, the standpipe should be a bit larger than the bulkhead (0.5" at least) if you wanted it to handle more flow.

Another thing you might want to try is put some eggcrate and plastic mesh at the end of the drainage line in your sump. This should break up the size of bubbles and help redirect the water away from the pipe. I've found that this stopped the burping in my plumbing and the bubbles created are diffused by prefilter foam. This makes a faint "fizz" sound but I can't hear it when the stand is closed up.

[outtafocus]

Originally the stand pipe was as tall as the overflow. I was testing to see if the height of the stand pipe had any thing to do with the burping. It seems this was not the case. I am picking up the new cap tonight and I will also pick up another stick of 1" pvc, I want to redo my return plumbing aswell.

As for the size of the stand pipe vs the bulkhead, it will have to remain as is. That slip to thread adapter is stuck in the bulkhead. When I picked it up, I was testing thread fit by hand and did not tighten at all, but when I went to remove it, it would not come undone and I didnt want to scar my bulkhead so I left it in. Now with it in the overflow I dont have the room to get it out. I am not worried about it.

[outtafocus]

I just added the full height stand pipe and began the process of trying to find the sweet spot with cap hole size.
All to no avail.
The system that seems to work best is the complete removal of the standpipe. I have just the adapter in my bulkhead at the bottom of the chamber. This causes no rise and fall, no sucking sounds and has great flow. The only downside is the distance the water must fall, this causes the loud waterfall sound, which I cant deal with being only 5feet from my TV.
I have one more plan I need to try before I give up completely. I will cut my drain directly below the bulkhead, leaving enough pipe to glue a 30degree or similar (I hope western pump sells) elbow. If I just use a 45degree elbow from that point the drain line will be in a very awkward position.
Cross fingers.

[Delphinus]

Strange .... I don't think it should be this difficult, I wonder what I might be overlooking here.

Just a suggestion -- on my 20g tank, I have an overflow in the corner, same style as yours (i.e., two glass panes in the corner). It's just a small tank so I didn't bother with a durso or stockman or whatever, I just have a standpipe with a strainer (strainer not really needed, just to keep the {now defunct anyhow} wrasses from going down the overflow pipe since they liked jumping into the overflow). The water level differential is only about 2" at most (I'd have to measure to give you an exact figure, but basically, it's a small drop). Since there's no waterfall effect, it's pretty silent, silent enough for me anyhow.

Anyhow, whatever the outcome, there is a way to make it quiet, keep at it, you'll find the groove that works best with a little trial and error..

[BT05]

It's too bad that the adapter won't come undone from the bulkhead, maybe use more plumbing tape next time? I know that Western Pump doesn't sell 30 or 20 degree elbows since I was just in there last week looking for some 3/4" ones. You might want to try out spa flex with two couplers to get whatever angle you need or use it for your whole drain line. There must be some wierd quirk about your setup making this difficult... I hope it works out, overflow noise can be frustrating.