Siphoning—a weighty topic

Will a siphon work in a gravitational field without an atmosphere, such as on the Moon or in an evacuated bell jar? Sure it will. A siphon depends on gravity and not on atmospheric pressure. Of course, you have to assume a liquid that will not vaporize in a vacuum and cause a vapor lock.

If you are siphoning water into a lake or gasoline out of a fuel tank, atmospheric pressure is a necessary condition to prevent vapor lock of those volatile liquids, but the pressure does not cause the siphon’s operation.