which firewall hose is heater inlet hose?

[slalomking]

Hey guys,

At 100K, I noticed the water temp needle is riding a tad higher and sooner than in years past. I figure it's high time to do a radiator flush on the Ecotec.

I placed Preston Flush 'T's in all my past cars but I guess my age and technology are passing me by. I cannot figure out which of the 2 water hoses coming out of the firewall is the heater inlet hose (location to place the flush "T").
They both lead to metal stems very close to each other which in turn are difficult for me to determine what the metal strems are attached to. (Yeah, I know, old geezer know nothing noob.. ).

Is it the heater inlet hose the driver side or passenger side hose? Also, is there any air bleeder valve or stem that would help get bubbles out?

Thanks in advance guys. Happy Memorial Day.