Here is my first attempt at an overflow drain. You are probably asking yourself did it work? Well the answer is yes and no. Yes the drain pulled water from the grow bed and drained it into the tank below. Yes the loop remained primed after the pump got turned off and the drain stopped. No the drain could not keep up with the pump. I have a 330 gph pump at 1' of head so i did the math and since the pump was was pumping up 3' it should be outputting approximately 200 gph. Since a 1" overflow should drain off 375 gph it made sense to me to go with a 1" pvc overflow.
Where did I go wrong? After review 3 things became clear 1) my lift is actually closer to 1' which means the pump is rated to pump 330 gph 2) this pump actually performs better that its specs indicate it should and it's delivering 400 gph 3) the overflow is probably only draining at 300 gph. Back to the drawing board, I will build a 1.5" overflow which should drain at a rate of 840 gph. Below is a not so good video that I shot in the dark with a flashlight on my phone, not good I know but it gets the point across. I will update when I get the larger overflow built until then I wish you love and happiness.