How to remove coolant in heater core when changing coolant?

My '07 just turned 100K miles and I am planning to change both the engine and inverter coolant. I would like to drain ALL of the engine coolant, including what's in the heater core, when I do this job.

I see in many posts in Prius Chat that a good amount of engine coolant (around 3 quarts I think) remains in the heater core even after opening all 3 drain cocks -- radiator, engine block, and the coolant heat storage tank (aka "thermos"). My question is, can the coolant in the heater core be removed by blowing compressed air into one of the hoses leading to the heater core?

Basically, I want to disconnect two hoses going to the heater core and blow compressed air into one of them so the coolant comes out the other one. But because the hoses at the firewall are not easily accessible (at least as far as I can see although I have not crawled under the car yet to really look), then where else could you disconnect the hoses to do this? And what 2 hoses would you disconnect?

I'm hoping this could be done at the "thermos", but would the "coolant flow control valve" between the thermos and the heater core prevent the compressed air from reaching the heater core?

Has anyone tried this? If so, what hoses did you disconnect? And did it work?

Please note that I am aware of the coolant vacuum devices like AirLift, MityVac, etc. but don't want to spend the hundred bucks or more for something that I will probably only use once.

Any input on the above greatly appreciated.

Also FYI, here is a link I found to EXCELLENT instructions and pictures for changing the coolant on both a Gen II and Gen I Prius that was produced by the Auto Tech department of Southern Illinois University. See page 45 for a good picture of the Gen II thermos and associated hoses. This document also has instructions for bleeding brakes, proper jump starting procedure, and a bunch of other useful info and pics. It also covers some other hybrids like the Ford Escape, Honda Civic, and Toyota Camry/Highlander hybrids. Check it out:
http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1016&context=auto_pres

PS -- To the moderators of this forum, could the above link (or the document itself) be added to the Knowledge Base?

 

Thanks but I don't want to flush it, just get all the coolant out. And really don't want to mess with removing the thermostat. And you're right, you would probably be left with just water in the heater core, thereby further diluting your 50/50 mixture!

And just a thought here...could some of the posts saying you only get about 6 quarts out when you open all 3 drain cocks be wrong? Did anyone get close to the specified 9 quart capacity when they drained their coolant?