Auto top off help...

[MikeP]

I set up my JBJ ATO system today. I have a siphon issue, when ever the pump kicks in (maxi jet 900) as soon as it turns off a siphon is created so water continues to flow from the reservoir into my sump . The tubing runs up out of the reservoir strait for a few feet and the down to the sump return. The tube is not submersed in the sump (as per the instructions). Can someone give me a quick physics lesson or trick on how to stop this from happening.

Thanks