Incomplete coolant flush but new pink coolant isnt mixing with old green

When I bought the truck a few months ago I noticed the coolant was green, so two weeks ago I flushed my coolant 5 times using distilled water. I didn't use the block drains, seemed like too much of a pain so I used the hose that connects to the oil filter. After the fifth flush, I was satisfied and put around 2 - 2.5 gallons. I left that bottom hose open when I started filling my coolant so it would push any old coolant or water out, but it didn't, just straight aisin pink. So I know that the remaining fluid (2-3 quarts if my math is right) is green. My plan was to drive it for a week or two letting the coolants mix and then I'd drain/flush and refill with fresh and do that until no green was left.

But it has now been two weeks and a few hundred miles, and when I drained the coolant both from engine and radiator, it does not appear to have mixed at all.

I thought that by now I'd have some mixing, the pink coolant I pulled out is barely darker than when it was new. I never drained or flushed the heater core as I was unsure of procedure and it had been two long weekends of working on the truck. I'm assuming that the remaining 2-3 quarts of green are maybe stuck in the heater core, but my heat and AC work perfect, so I doubt its clogged. If I actually did manage to get all the old green out then my new coolant would be mixing with distilled water, but it doesn't appear to be diluted at all.

Any advice? I know that the mixing coolant can cause some serious headaches that I'd like to avoid.

 

Continue flushing with distilled water, and use all available drains

 

Also, see @bfunke’s quality reply ITT: https://www.tundras.com/threads/screwed-up-and-used-the-green-stuff.151230/