Coolant Flush How

[GTSailor]

I have read on here a lot about coolant flush but I am still not sure of the exact method to ensure the whole system gets flushed. I drained my coolant and it got increasingly more dark red (like rust) and even looks like coolant types were was mixed (green vs. red).

My concern is mainly getting the heater core properly flushed and air purged out each time I drain the system and fill. When I initially drained it I thought it was done and i pulled some fittings off where previous owner had tied the "in" to the "out" when he removed passenger heaters and there was still a lot of coolant left. Then I realized there is a high point where the two hoses go through the fire wall. (Aside: I plan to cap these which will make coolant actually go through the core instead of basically bypass the heater core.)

So questions:

1. Assuming in pic that valve A is the discharge of the coolant pump, B is the return to the pump with its own valve and maybe C is for purging. When I fill each time prior to running engine, do I Close B, Open A, and purge out of C until full, then open B?
2. Should I high idle the engine to minimize low load idle and to get t-stat to open and is there a way to detect if radiator is full / Heater open?
3. I noticed rust on my tstat, inside bottom heater hose, inside top heater hose, etc. I was thinking i probably need to use some sort of coolant flush product. Any suggestions?
4. Is there a way to use a hose and continually bleed water out? like maybe even through heater return valve B? Maybe use the other end going to pump to hook up water hose to pump inlet?
5. Generally speaking i have read here to fill with water and maybe some liquid dishwasher soap, then run, then drain; fill with water, run, drain; repeat until drain runs clean; final fill with choice of coolant at proper mix (i am going ELC with no additive filter).

Ultimately I feel like there is a slick/simple way to do this with all the ports and access to maximize flushing effectiveness (I have high pressure and low pressure coolant on block for air compressor - but only could use if engine/compressor not running)

[HamSkoolie]

My F350 pickup has the 7.3 Ford PowerStroke (essentially the DT444E from IH). The procedure used for that engine is to drain (and drain the block via two small plugs at the bottom of the block). I then filled with tap water and ran the engine until the TStat opened. Then drained (including the block plugs) and filled with DISTILLED water, ran until TStat opened, then repeated with distilled water.
I then poured in CONCENTRATE Extended Life Coolant (ELC) approved for my engine. I added 1/2 of the total capacity in ELC then topped with distilled water in the same amount. Ran the engine, tested for concentration level with dip strips, and did final topping off with 50/50 (concentrate and distilled water).
It's a bit more complicated with buses that have long hose runs for interior passenger heaters (or RE's that need coolant to the dash area for defrost and driver heat) but similar.

Your 466 probably has similar block drain plugs. When I first pulled my plugs there was a good amount of "sand" that came out from the bottom of the block so it's a good idea to pull any such plugs and it also gets a fair amount of liquid out.
Not the same situation as yours but hopefully this gives you some ideas.