how well do check valves work?

[jacksonpt]

I'm going to be setting up my overflow boxes, sumps, and related plumbing this weekend. I was wondering if it was worth using a check valve to prevent water from being syphoned into the sump if the power goes out. Do check valves work very well for this purpose?

 

[barracuda]

Why not just to drill a small hole in the return line pipe just a bit higher than the water level in the tank? Simple one!!! Thsi hole will break the syphon.

 

[scotts]

I have to agree with these people. In an industrial environment I will always put in a check valve. (I used to run the maintenance shop at our plant). However in these little systems for aquariums I would recommend the the drilling the hole thing.
Scott