GPH return to sump.. not good

[skunkreef]

Guys.. I took a 1 gallon container and timed it to full.. it took about 22 seconds. I am guessing that I only have 160GPH comming out of my sump. Its a overflow in a Marineland tank and I set up a durso pipe. The durso is 1 1/4 and the drain is 1". If I turn the return pump valve up I pull the sump dry... My return is a Gen-X 6000. I know the 1" drain should be able to flow 600gpm? Any help would be great! Thanks! BTW I have a ton of air being pulled down the overflow draining into my sump.. any thoughts? Its hard pvc to the sump. I used 45's for the angles.. and it has a nice smooth slope.