I've done lots o' things to try and "tweak" durso pipes. One that I found to work real well is drilling the hole large enough to insert some flexible airline tubing. Attached to the end of the tubing, is a plastic airline valve, like this: 
You can then adjust in tiny increments to see what works.
Dave
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"Fins to the left...Fins to the Right, I'm going home to play with my reef tonight..."
If you're looking for me, and I'm MIA from the board, email me at JustDavidP (at) gmail (dot) com.
Experience in aquaria, 35 years. Experience in marine, 20+ years. Experience in Reef Keeping, 6 years. Always a newbie! | 
