Thanks for the tip, agreed.squint;1374482; said:I just setup a Durso in a small (75 gal) "reef ready" tank. I am also dealing with 1" bulkheads and used 1" PVC. I found that the Dursos really aren't that quiet. So far, my best result has been from drilling a single hole in the top plug and inserting a length of airline tubing. I tried to keep the amount of tubing above the waterline to a minimum. But I still had to have enough so I could adjust the height of the lower end of the tubing. By adjusting the height of the lower end of the tubing, I could tune it.
I also came across the airline trick on the net during my 'quests' for silence. It actually helped my 1" pipe as well, although made little noticeable difference on the 1-1/4". Once I realized that 1" is simply problematic, it dawned on me to submerse 1" and not bother with the durso for that size pipe.
I then attempted to submerse both (with ball-valve restricting), but balancing equilibrium seemed scary. Trying to balance just enough restriction to be 1" over the pipe, too high and were running the pumps dry, too little and it's loud. Next step would have been CHOMPERS 'net' thingy, which I never got a chance to try, since it finally became silent.
By submersing the smaller pipe, cutting a couple of inches off of it (so it's always an 1" below the durso's water line), and restricting it with a ball-value, it was silent. For the larger pipe (1-1/4) I used a Durso (to handle extra flow), surprisingly didn't need the tubing on this size, and with a slight ball-valve adjustment it was mostly silent.
The (2) Quiet one pumps (which are relatively quiet to other pumps) are the only hum that I hear now, minus just a nice flow of water background sound. Although maybe I've spent way too much time listening to this thing, where it's starting to sound good, grin.
Ed