IIRC, you actually want to build the durso one size larger than the bulkhead and adapt it down where it connects. That should give you more water in the durso than it needs, helping to reduce the noise and improve the flow.
Build your own Durso Standpipe ™
"My tank has a 1 inch bulkhead on the bottom glass where the water drains out. For this size hole, I recommend you use 1¼ inch PVC for the standpipe. I do not recommend 1½ inch PVC as the larger fittings are much harder to fit inside overflow chambers. And secondly, there is no advantage in 1½ inch over 1¼ inch PVC when dealing with a 1 inch bulkhead -- the bulkhead is the limiting factor for the amount of water that can drain out.
With 1 inch and smaller bulkheads the standpipe PVC diameter needs to be larger than the bulkhead to work correctly. I get a lot of e-mail questions on why this is. Honestly, I'm not sure. Typically if you use 1 inch PVC pipe on a 1 inch bulkhead you get poor results. (Some exceptions with smaller low flow tanks.) Take my word on it and use 1¼ inch PVC pipe. For large tanks with 1.5 inch bulkheads and large return pumps however, there does not seem to be any need to oversize the standpipe for larger bulkheads. Larger bulkheads can use PVC pipe & fittings that match the size of the bulkhead. (I consider tanks in the 350 gallon and up good candidates for 1.5 inch bulkheads)."