I just set up a bean animal and using just aquarium air line my secondary drain would hold siphon, ended up using 1/4" hose to stop the siphon. I figured an air break was an air break. On my old tank I had same issue with the small water stream as you, I added a small piece of tubing that I angle cut and put back of angle toward water flow to stop it, kind of looked stupid but it seemed to work for almost 2 years