PVC overflow

[RDNanoGuy]

Without a small hole the overflow will create a full siphon and drain the ubend causing the siphon break. That's why need the hole. The needle valve will help dial it in. It shouldn't whistle with the valve in place. Also set the output of the drain about 1 -1.5" below the water level in your sump. That will silence splashing noise but still allow the water to push excess air out of the pipe.