so i used to have just 2 small 1/2 inch overflows but they wern't going fast enough for me so i decided to build a 3/4 inch overflow out of pvc
and i had some pipe left over so i built 2 more, and im shure glad i did. for some odd reason(they work fine now) 2 of them decided to stop working. if i didn't have that third one i would have had 10 gal
of water on my water. just goes to show that redundency is great.