You probably have the drain hose shoved way too far down the drain
pipe. Your drain pipe should be around waist height, and the drain
hose shouldn't stick more than 6" or so into it. But in reality,
whatever stops the siphoning is fine. If you can't adjust the drain
hose for whatever reason, there are anti-siphon assemblies for purchase
that will cancel siphoning, but why add one if you don't really need it.