Well, that doesn't depend on how much fluid there is, if there is no air inside... But anyway, I was just shooting out a random idea what I meant was that while using a pipe designed for liquid cooling, maybe someone could figure out a way to use the same pipe as a heat pipe. I'm not saying it's doable right now, but IMO it would make sense in the future, which is what I was discussing here.
It's very simple, just connect a tank of fluid together with the pump lol... A tank is needed either case, because where else would you put the fans?
That's why the connection wouldn't be very simple. When disconnecting the pump, it should depressurize the heat pipe to make it work without a fan.