like they said, you need an overflow box or a weir.
we dont have a siphon to the fuge / sump area. it is gravity fed.
there is only a siphon in the overflow box portion.
What I did was I studied all the pages at melevs reef, posted a couple of posts here, then built my own.
I used 2 lees specemin containers and some pvc pipe to construct mine.
Small specemin box for inner, and large specemin box for outer.
the overflow box is constructed such that only a minimal amount of your main tank can drain into it at a given time.
The overflow box is built in 3 sections - the inner box, outer box, and u tube.
the inner box hangs inside your tank, just below the full water line.
the outer box hangs outside your tank, and hangs deeper than the inner box, because it is the large specemin container and is built deeper.
the u tube will create siphon between the inner and outer boxes.
Then from the outer box, you have a gravity fed pvc drain down to your sump.
Your return pump can run as fast as your overflow box can drain.
go big on the drain size. 1/2" drain was ungood. 1" is OK for a 300gph pond pump from lowes, but barely. 2" drain and i could have moved some water volume.
but you have to study the design.
im leaving out important details.
