Man Made Live Rock
The Modified Durso Standpipe that I use has served well and not caused any trouble at all once the noise issue was taken care of. The first one I made was built using Richard Durso's instructions.  While it did keep the water level in the overflow high, it sounded like a freight train, or actually like a freight Drain!  No matter what sized hole I used or how hard I tried it just would not stop sounding like a flushing toilet at least once or twice an hour.
Now it could be said that there is the possibility that I wasn't doing something right, but let me assure you I really tried to make it work.  I tried any and all suggestions I could find to make it work, but ultimately tore out the original in exchange for not less than 5 others of similar design.  I tried longer and shorter hose, fatter and skinnier PVC, I adjusted the height of the standpipe several times, in short I played with many variations.  I finally stumbled on one that works for me.  I think it is actually a result of various things working together as opposed to a magic bullet.
There appear to be several areas of concern when building a standpipe that may just fall into the category of an art or magic rather than science.  The troubles I had with the original were dealt with from top to bottom.  The first was the slurping sound coming from the intake.  Then was the whistling sound from the air intake, then the gurgling and flushing sounds coming from within the pipe itself and the sump area.
I would not want you to think that you can just build what I have and place it inside of any tank and it will work.  I do not know if it will or will not.  It could take considerable tinkering to get a setup that will work for you. What I have to share is just my experience with standpipes and many attempts to get them to do what I wanted. What I do know is that it works fine on my Oceanic 75 Reef Ready that it was built for. I have used pumps from 300 to 1200 gallons per hour on it with little noticeable increase in noise so I am fairly certain that the design is good. I just cannot say it will work in any and all cases.
It is interesting to note that Oceanic tells me they suggest the "maximum recommended flow is 800 gallons" on the 75RR apparently for the noise reason. Yet they did tell me the teeth and bulkhead can handle at least 1200 gallons per hour but "at that rate you will have a disturbingly loud setup". I currently run it at 900 gallons and unless the sump volume gets lower than the output from the Spa-Flex my Bionic eared wife doesn't raise the issue. The power head breaking the surface of the water is louder than the overflow and sump areas.
Near as I can tell there are a few key ingredients that worked for me. They are listed below in no particular order.
First up on the quite the standpipe crusade was the whistling that was coming from the air entering the standpipe. Figuring that since the sound was coming from the top, I had better concentrate my efforts there. In short the whistling stopped as soon as I quit using the large white caps that are specified in the original plans. I swapped them out to a threaded fitting that happened to have very inexpensive caps. Since I didn't have the correct sized bit for the rigid tubing I had to go with a smaller one. Tilting and turning the drill with the small bit to get the hole just a bit larger simultaneously killed the whistling sounds that had been coming from the large white cap holes. I would presume it would have something to do with the angles involved, but I am not a whistle building expert, so that is just a guess. The outcome was a total accident, but a nice surprise none the less.
I would like to say that extending the rigid tubing down past the bulkhead was an act a genius on my part. But it was not! Somewhere I had read that using a rigid tube would stop the sound from the top end of the standpipe. It did not do that for me. Swapping the 90 degree elbow to the 45 degree did however eventually stop the top end from slurping. So I was trying all sorts of lengths of rigid tubing trying to get the slurping sound to go away.
I was frustrated that all the lengths that I tried were not working. So I took my last three foot section of tubing and made the bend, to stop it from falling down the standpipe, just like I had before. While deciding how long to cut it off this time I just set it down the hole in the top of the standpipe. It hung on the bulkhead sticking out a good 8 inches or so. I sat down on the couch just looking at it, trying to think of how short or long to try this time. Maybe several minutes passed and the standpipe did it's normal gurgle and flush. This time however the gurgle knocked the tubing loose. It fell down past the bulkhead. Ahhhhh, the silence was deafening! I couldn't believe that it was gone so I waited at least an hour before removing the tube to trim the bend portion down to size. Then I replaced the tubing, wiggling it past the bulkhead. As soon as I did the gurgling stopped again, now the sump area was quite at last.