99 lumina 3.1 heater core inlet hose

Hi everyone. This is my first post here. I'm working on a 99 Lumina with a 3.1 liter engine. I want to install a backflush kit but I'm not sure if I'm looking at the right hose. They say to put the tee in the heater core inlet hose. The hose I'm looking at is coming from the heater core and connects to metal tubing which runs along the front side of the engine and goes to the water pump. A rubber hose then comes off the water pump and runs to the top of the engine. Is this the inlet hose? The Haynes manual doesn't tell me anything about which hose is which. If that is the right hose then I have plenty of room to install the tee on the rubber hose at the firewall. Any help is greatly appreciated. Thanks in advance, Mike

They say to put the tee in the heater core inlet hose. The hose I'm looking at is coming from the heater core and connects to metal tubing which runs along the front side of the engine and goes to the water pump.
I'd expect the hose from heater core to water pump is the OUTLET of the heater core. Any chance it's larger than the other hose that's attached to the heater core? The larger hose (if there's a difference in size...sometimes there isn't) is also typically the outlet hose.

The inlet hose is piped with metal tubing from the chevy flow restrictor, just behind the thermostat housing on the lower intake manifold, that makes an s-bend and then transitions to rubber hose. It's lower than the heater core outlet hose of which you speak.