99 prerunner 2.7L - radiator flush question!

Hello. I recently flushed out my radiator and ran some water through to try to clean it out. When I added new radiator fluid, I only used a gallon of fluid and the radiator was full. I then started the engine for a minute and then added a little more fluid and it got full. Is this normal to only use a gallon of radiator fluid to completely fill the radiator? I was told that it took 2 gallons. I also wanted to mention that when initially added fluid, the car key in the ignition was turned to the ON position but the engine was not turned on itself (must have left the key in ON position and on neutral because I had previously pushed the car to move it). Is this normal for the radiator on 2.7 to only use a gallon of fluid? Thanks

 

I think you might have not drained the engine block via the drain valve just under the exhaust manifold near the front of the engine. It's a little hard to see at first. There is a small spout facing downwards with a bolt on it. I think it's a 12mm or might be a 10mm.
Opening this will get more out.
I use a flush machine at work. Do mine every year and it takes about 2 gallons. However, the machine will push as much as I place in it before it stops. I use 3 gallons just to be sure everything is out.

 

X2 on the engine block drain plug. 12mm does sound right... it was 3 years ago for me though. You can also squeeze the radiator-to-block (cold) hose to help remove some remaining coolant when you drain (might not be necessary for a flush though). Also don't forget to use a mixture of coolant/distilled water.

 

Thanks for replies! When I drained out my radiator, all I did was remove the drain plug from the actual radiator....I didnt know there was another drain plug -this is probably why I only was able to add 1 gallon. I probably have another gallon of old coolant still in the engine. Damn it! Now I'm going to have to do this process again...well I guess this is how you learn right? lol

Where is this other drain plug located? Does anyone have pics of what this drain plug looks like and where its located? Do you think I may have damaged anything flushing the coolant the way I did? I also ran a water hose through the radiator for a good 5 minutes. Do you think I may have gotten water in the block where the other coolant is? I'm going to need to redo the whole process tomorrow. Whats the easiest way to access this other drain plug and do I access it from the top of the engine or do I need to crawl under. Thanks! Also any tips would be helpful too. What a fail I did on this

Forgot to mention that I used a 50/50. Is the 50/50 better then pure coolant with adding water? thanks again guys