how to prevent flow-back from return pipe?

[cgrant]

I turned my pump off for a couple of minutes and noticed the water started to flow backwards into my sump from the return pipes, I freak'd and quickly turned the power back on.
how do you prevent this?

 

[irondog]

You need to drill alittle hole in your return coming from your sump into your tank,like 2"below water line,once you have hole there you should be good

 

[jhov2324]

i have the hole also, but just to be safe you should get a check valve, install it into the return line tube,

 

[nm reef]

Drill a small hole in the return line just below the water level....as the water level drops air will enter the hole and stop the back flow. Breaks the syphon ... just be sure to keep the holes clear and whenever the pumps are down they'll work like a charm.

 

[turningtim]

IMHO, A check valve may fail in time and usually at the wrong time. An antisiphon hole is the way to go. 2" is a bit low. As NM stated just below the water line maybe 1/8" - 1/4" will work and keep it clear.
HTH
Tim