<a href=showthread.php?s=&postid=11610617#post11610617 target=_blank>Originally posted</a> by ReefWreak
Make sure that if you've got a clear checkvalve, as most are, that you don't have a refugium grow light near it, as I've had algae grow in my checkvalve, and as a result almost flooded my sump. Now I've got both the check valve as well as my outlets at or above the water line so they can't siphon back, but I guess you don't have that option :-/ oh well.
Maybe double check valves would be a backup? or drain to outside if possible like Rogger has/