How much coolant do you put back in after flush?

I have a flush tee on my heater inlet hose. I will be doing a backflush than drain out remaining fluids from radiator. Does this method apply?

Can blow air through inlet hose to push water out?

Thanks.

I had to do 2 vehicles. A GMC Jimmy and Ford expedition. I could not remove drain plug from GMC jimmy so I removed lower radiator hose but ford was easy to remove. After draining, I previously had a prestone backflush kit installed on both vehicle heater inlet lines and used a garden hose flushed water through them until I saw clear water. Then drained radiator again. Then I add some prestone "flush" and added water back up to reservoir full line and ran engine for 15 minutes. I flush again and added just water ran engine for another 15 minutes. Lastly, I flushed and added just about 1.5 gallons for gmc jimmy and 2.5 gallons for Ford expedition coolant. I let engines run for about 30 minutes with cap off reservoir to let system bleed out air and add just coolant. As you said earlier, it would not take full capacity because of diluted water in block. Both vehicles run good sofar. Thanks.