Yep. It's easy to test for yourself that a siphon will quickly stop working if you let too much air into it. This is also why you can't make very tall siphons,

Yep. It's easy to test for yourself that a siphon will quickly stop working if you let too much air into it. This is also why you can't make very tall siphons, as if the pressure gets too low at the top the water will boil off, create a gas pocket of water vapor, and stop the siphon.