Doing coolant flush right now.

I am referencing several tutorials on the website:
1. Official Coolant Flush Guide
2. https://www.youtube.com/watch?v=oQsxmi-CNng
3. How To: Coolant Flush - PICTURES!

Everyone of these people are able to get around 8 qt out of the system. I am only able to get 4 qt (1 gallon). Not sure what is going on.

The process for drain and fill is pretty straight forward: drain old coolant, refill with distilled water, drain distilled water 3-4 times, refill with new coolant mixture.

The car is 2010 4Runner Trail Edition. I have flushed the system this way with around 4 gallons of distilled water and refilled it with 50/50 coolant mixture. The concentration is very alarming right now.

Why am I able to drain only 1 gallon every time, whereas others are able to drain 2?

Thanks. Any help would be appreciated.

Are you draining the engine block also or just radiator?