As far as 24 hours, yes, it does sit for 24 hours.
Here is the metziyus. You have a big barrel of beer which is pressurized. You attach the tubing to a port on the top, and open the port, allowing the beer to flow through the tubing until it is stopped by the valve at the end of the spigot. When you want to pour beer, you open the spigot and the beer is forced out.
I imagine the entire body of beer being connected to itself within the tubing and barrel.
And you are correct about the answer to itche’s sfek sfeika. It is all one safek.