So overall, you have your overflow, which sucks up the water that goes above its rim, that water goes into your wet dry, which then gets pushed back out to your main system. Right now you have too much water, your water level in your system is going to stay at the same level as long as your running your system. The water from your overflow is going to push all the water it gets into the wet dry, which then re-enters your tank. So what your gonna wanna do is fill your tank up, all the way up to the brim of the overflow, and then fill your wet dry up as high as you want it, and then plug up your return pump and start your siphon. From then on out, your golden. I have an aqualifter on my overflow just to get air bubbles out, and occasionaly it gets clogged with something so I have to blow out the siphon tube and replug it into the aqualifter. Let me know if you have any more questions and if this helps at all!
Steve