Durso Pipe - what size pipe?

[DJ88]

If you are using a 1.5" bulkhead you don't need to go up to or reduce in size at all. As long as there is a bend in the line heading to your sump that will create the backpressure necessary to keep the durso quiet. I had a 1 1/4 reducer in my durso from a 1.5 bulkhead and took it out to see if it operated differently when I was testing my ampmaster3K. No change.

If you are running a smaller bulkhead the reduction is necssary. All you will do by adding in the reduction after the bulkhead is reduce the max flow of your durso. In this case.