I use 1" PVC
because my pump has 1" outlet on it and I did not want to reduce it and introduce backpressure.
I go out of the pump at 1" PVC
and then go thru a 1 way flap valve to protect against power outages. Then I convert to plastic tubing (to reduce vibration) and then convert back to 1" PVC
I then go thru a "T" connector to split off the return into two. I plumb these to either end of the tank. I use a combo of 90's to get up and over the tank. I use 1 90 elbow on the end to direct the flow a few inches below the surface of the water.
My flow goes from the back corners in the direction of the front middle of the tank.