Looking for advice on flushing the rear heater core on the 1996 6.5 diesel Suburban.

I have a black and a green hose going to the T's from the back of the Suburban. Which hose is supply and return?

Or I have a top and bottom T - Which T is the supply and which is return?

There was one line coming off the thermostat housing to one of the T's. Is that the supply?

How much pressure can be used to flush the system? 15lbs? 8 lbs.?

It seems to me that it is Ok to back flush the system as well? Is this correct?

I know there are some old threads on this someplace, but I have not had time to look yet.