Return Line Siphon Break
 

For those of you with drilled return lines either through the back of your tank or inside your overflow, where the return line never actually goes above the waterline, how do you prevent siphoning when the return pump shuts off? do you rely on a check valve? or is there another method im unaware of?

i use a hole drilled in the return line just below the water line. on the old 175g my returns came up through the overflow box so i have the anti siphon hole drilled in the line in the over flow eliminating the possibility of bubbles in the display.

but what about the tanks that are like 3 inches below the water line? I have pvc coming over the top of my tank as its not drilled, and i drilled holes just below the water line as well, but there are some return lines that come nowhere close to the water line.

Not sure what they do then. For me in absolute worst case sonario the display can drop almost 5" if my drains failed to hold water my sumps can handle it. I'm not sure what others do myself I wouldn't rely on a check valve unless they are maintained regularly as they are prone to malfunctioning.

I've only ever seen lower output holes used for closed loop and not a return lines for this very reason. However you could still add a syphon break... but the plumbing won't look very pretty. Here is an idea I sketched out. If I was more ambitious I'd learn google sketch but not today. Good grief this looks awful... But anyways, just close the ball valve most of the way to only allow a trickle through. When the power goes out that top part will break the syphon.

http://i254.photobucket.com/albums/h...ps8362537a.jpg

You could just put loc-line on and direct it so that the output is just below the water's surface.