Heater hoses: Which one is the "inlet"?

[Jesda]

3rd gen MaxVG30

I'm installing a T-fitting to flush my heater core. The instructions with the fittings say to tap into the inlet hose. Which hose is the inlet? Is it the upper or lower one coming out of the heater core?

[maxhopper]

I believe the inlet hose comes from the intake manifold, and the outlet hose goes to the throttle body (not sure which is top and bottom).

[xsblacksx]

*I can't add anything useful to the topic at hand*