OED is right
It's not due to gravity, a siphon works INSPITE of gravity, if the gravity is to high a siphon will not work, but as long as there is air pressure (atmospheric on earth), a siphon will work. Gravity or not.
If fact, a siphon will work perfectly well in zero gravity, the h or maximum height of the 'hump' would be infinate.
Air pressure pushes on the surface of the liquid, that pressure if great enough will push the liquiq uphill, against gravity.
On earth the air pressure is created by gravity, but the air pressure does not have to be supplied by gravity, it just is on earth.
On the space station, where there is air pressure but zero gravity, a siphon will work just fine, again the h value would be infinate, if the available air volume, and liquid volume were also infinate.
A the fluid moves out of the container the air pressure on the surface of the fluid will lower, on earth you would not see this effect because of the large amount of air available, and the flow from source to destination and destination to source for the air.
But a siphon would work in zero gravity, if the air pressure was supplied by cylinders or compressed gas for example, or just the normal atmospheric pressure within the space station.
The human circulation system relies on a mixture of pumping and siphoning effects to circulate blood through the body, but when astronaughts to go space, they dont die. The siphon effect works in zero gravity, and blood keeps circulating.
Cooling system no the space station would most certainly rely upon siphons to move coolant.
There is no 'vacuum', a vacuum is an absence of stuff, not a 'thing' in itself, if there is air in the siphon pipe it will not work because gas is compressible, and liquid for most part is not. thats why you have to fill the tube of a siphon will fluid before it will work.
So this 'so called physist' is completely wrong and OED is right, it's odd that someone that calls themselves a physist would not simply revert to math, and look at the equation for a siphon,
Bernoulli's Equation, and look at the terms that it uses to calculate a siphon, gravity is not a factor, density is, P is pressure, h is height