Custom Aquariums has been granted a United States Patent for the Siphon Stopper aquarium output nozzle, which minimizes the risk of a back siphon from the aquarium to the filter sump without reliance on failure-prone check valves.
According to Custom Aquariums, the advantage of the Siphon Stopper design is that no seals are required to break the back siphoning of water from the aquarium in the event of a return pump failure or power outage.  The Siphon Stopper works automatically when air enters the Siphon Stopper cap when the flow of water is shut off.

No matter what height the output nozzle is positioned under the water, the Siphon Stopper cap sits at the water line and will break the back siphon. Gravity will MORE