first time setting up a durso stdpip

[Kayleb]

I finally got my 75 together, I had the back glass drilled for a 1 1/2" bulkhead. I built a durso and installed it. I set up a temp. sump just to place my pump and returnpipe in just to get everything flowing. However
the durso won't drain fast enough for the pump which should only be pumping aprox. 750 gph. The I.D. of the elbow going into the bulk head is 1 3/8". Also How do you attach pictures to posts?

Any help is appreciated!