The first thing I would try is a 2" standpipe. It'll be the quickest and easiest fix and give a better idea where the problem lies.
Another idea would be to install a Tee directly below the bulkhead and run the branch line up and then down into another section in the sump. Next install a valve just above the sump on the main drain line. Closing the valve will cause the drain to fill with water stopping air from entering the sump. You'll want to adjust the valve so water just starts to trickle out the other drain and the back up the valve a tiny bit. This will work similar to a herbie overflow but only needs one drain, it won't be as quiet as you'll get noise through the second drain line as it's connected to the main but you should be able to muffle it.

Thanks for all your ideas. I'll try some of them out this weekend.

My tank makes a huge amount of noise but if I tune it just right there is no noise. I have a 1-1/2" pipe with a basket. The thing though is I have a piece of airline zapstraped to that and just adjust it up or down to make the noise stop. If for some reason the hose clogs. (I keep it at the max height I want the tank to ever be) then the water gets sucked right down fast with tons of noise alerting me that there is a problem.
Hope that makes sense.:smile:
Maybe a small piece of hose is all you need.

sphelps, didn't you have a drawing of that and if so could you post it up again

I remember this battle. It took me some time to understand how my Durso thinks. It wanted many things before it would shut up. Now we have an understanding.

The trick with a durso is that there has to be enough air entering the standpipe to avoid a siphon. If a siphon forms, you'll get "flushing". Backpressure also can create flushing, as air will get trapped in the standpipe as Hairytank points out.

I don't know how loud is "too loud" for you. A durso will never be dead silent like a herbie, because there is air in the pipe and that creates turbulence both in the pipe and on entry to the sump. There's no way to make that go away completely, but it certainly can be tuned to be reasonably quiet. In my living room, the drain is just slightly louder than the return pump hum, and that's good (I like water noise more than pump noise).

A closeup photo or two of the durso and the sump entry would probably help.

Add an extension piece onto the return pipe going into the sump so it extends 6-8 inches below the water surface. That way there is no "waterfall" noise.

That never worked for me but then I don't have a dorso.
I do think the air into the top is the key.

I think Matt has the right idea,

Great idea I would try this on mine but I don't have enough room for that now.

I would say get rid of this cap and put on one with a single 1/4" piece of hose that you can adjust up or down, and if that does not work you might want to look at changing some of your plumbing Sphelps way.

I think he means something like this??

http://i103.photobucket.com/albums/m...sman/drain.jpg