In your very first post in this thread, you wrote.....
2. the diameter of the stand pipe. I have used 1/2"PVC and 3/4" pVC. Each diameter will drain the bed faster that it is being filled.
Was this 'with' the media in the grow bed...?

Now your saying....
Quote Originally Posted by flienlow
I think the issues is that I have more inflow than outflow. When testing again without any media in the tank, I had a good siphon, but the siphon would not out pace the infill and reaches a steady state at half way.
Try testing 'with' the media in the bed.
If you then have too much in-flow, you can split the line comming form the pump...and send it elsewhere.