it should work with the t, what it seem from the first post was that you were using valve to limit the flow out of the tank, what i what i was getting at was let say your valve on the "to sump" side of your tank has limited flow with valves to 200gph. if your pump to the aquarium is at 600gph, the extra water has no where to go exept on your floor, or if your lucky your sump will go dry.
more or less the gph into the sump and out to the tank should be the same