Questions regarding LT1 cooling system

I know this is gonna sound remedial, but here goes......

How does the sealed system work on our lt-1 cars?

Specifically how does the water pump not pump all the coolant up and out of the coolant tank when the cap is off and car is running at cold idle?

Also what does the little 3/8 line on the top of the coolant bucket do? I know it goes to the TB bottom but what's it's job? Some tanks I have have 2 barbs on top (forget why there's 2) can this line be blocked off?

Swapping the non-Capped radiator and bucket into the c-10, have everything plumbed except that little line and I having some nervous thoughts about the tank exploding with coolant.

Any info is greatly appreciated

You can cap the second one. It was used on '94s and omitted later on, it went to the radiator.

So a 94 radiator will have a barb on it for that line?
Was it a Caprice only thing? The radiator and coolant bucket I have in the truck is actually from a 94 fleetwood and there is only one barb on the tank and no barbs at all on the radiator.
What about the other one? Do I need those lines at all?
Is it a return line? Whats it actually do?

The one they all have is used to keep the TB warm by passing from the steam pipe thru the TB & back to the overflow.
The bypass takes it from the steam pipe running up the pass side (between valve cover & intake) & sending it directly into the overflow.
I think the idea is to allow any air to stay up high in the circuit
That allows the air pressure (expansion) to be delivered on top of the fluid
It doesnt pump down because the systems full.
If the cars allowed to get hot (without a capped tank) the fluid will rise & overflow (if overfilled)
I think thats what I know

I get ya, at first I was like how the hell am I gonna do this???? There's just not enough connections, and which way is push/pull????
Then I thought about it and was like "it's gonna be the air trapped inside the tank that pushes the coolant and keeps it out of the tank"

So if I was to hook this small 3/8 (or whatever size it is) line up someplace on a gen-1 engine where should I try to do it?

Right now I have it like this:

Top radiator hose= thermostat housing
Bottom radiator hose= bottom of water pump
Top heater hose= top of water pump
Bottom heater hose= passenger side front of intake manifold. On this connection mid line I have a tee that picks up from the bottom of the reservoir. And then I have the small 3/8 line loose for now.

Should I not start the truck with the cap off EVER? Or is it gonna function like it would in an lt1 car? To me it seems like the water pump is gonna pump into the heater core, back out of the heater core and then go to the intake AND reservoir until the damn thing overflows. Unless having a correctly filled system prevents this???