I did what kgross said.
I first used a peristaltic pump and tubing. This was problematic due to siphoning, failure of my peri pump to prime, etc... I switched over to PVC and a little power head.
Here is how my old sump and ATO worked. Never had a problem.
I also drilled a few holes along the resevoir side of plumbing to create many air breaks, just to be sure.
Obviously, some of the water just ciruculates through your bucket.
You can use this to your advantage to control how fast the ATO fills your tank. This can vary depending on what type of controller you are using.
Ryan.