you can pass out almost immediately
I hate to pop anyone's bubble, but I wouldn't put too much reliance on that "immediate" thingy.
I know there is information out there that indicates it can be immediate,
but users on this thread have experienced anything BUT immediate.
In fact TiredHorse, the person who started this lengthy thread, experienced a delay so long that his SI kicked in, and he removed the mask.
This happened several times. He was indeed frustrated.
TiredHorse was also knowledgeable about firearms.
Certainly no delay there, so long as SI doesn't prevent you from pulling the trigger.
Nobody knows what ever happened to TiredHorse, he just disappeared from SS.
I suspect he either gave Exit Bag another try and was finally successful, or possibly used a firearm, to which he had hinted at.
He was not the type of guy to ghost SS, for which I draw my assumptions.
The famous Smilla, also had problems with SI due to long time waiting to go unconscious.
She was finally successful, as explained in a more or less indirect way by a friend of her's.
Inert Gas/Exit Bag was once my method of choice.
I read all the literature about how immediate it was. This was the reason it was my choice.
I was disheartened by all the people who indicated how long it took to go unconscious.
I have since decided to give life another try.
If I have another change of heart (been there before), SN will be my method of choice.
what's to keep the Argon from flowing out of that same space?
Nothing! The Argon does escape out the bottom of the bag, which is why you need so much gas.
what forces the CO2 to leave and not hang around
The difference in the specific gravities of the two gasses.
CO2 is heavier than Argon, so it sinks to the bottom, and then forced out of the bag by the flowing Argon gas.
Does it matter what position the tank is in?
No, the tank, valves and regulator will work in any position.
The flow control, if the type using a ball bearing, will need to be vertical, as it relies on gravity acting on the ball.
The only thing important here is to prevent the tank from falling over, which could possibly disrupt the process.
Sound like the tank would be pretty safe reclining next to you in the bathtub.
A note about using Argon:
Now I know there are people who will refute me on this,
but the difference between the specific gravities between CO2 and Argon are VERY small.
This make me question how well the CO2 will drop to the bottom, and exit properly out the bottom of the bag.
This method was originally design for use with helium, which is much, much lighter than CO2.
But helium became scarce, and balloon gas people started mixing regular air with the helium, which defeated the purpose to ctb.
There is still a significant difference in the specific gravities between CO2 and nitrogen, so I would recommend using nitrogen.