On 1968 C10 heater core which tube comes out the top of the heater box?

[HeavyHauler]

Originally Posted by PbFut

Pressure to the bottom of the core. This forces air out the top. If you run pressure on the top you are trying to force air downward in the core and making the bleed difficult. Years vary and so do water pumps, manifolds, and radiators making the plumbing a challenge at times.

According to the diagram above the pressure side (water pump large hose) goes to the top while the (intake manifold connection small hose) is at the bottom. The diagram pic seems the opposite of what you are saying?