Alright here's that diagram I promised. I cannot stress enough that you need to ensure that the coolant tank has fluid in it at all times during this procedure. If it begins to go low on you stop and fill it up.
The pipe I enclosed in red is what we're using, disconnect the hose clamp circled in green.
Ensure the vehicle has warmed up to operating temperature, turn it off, slowly loosen the overflow tank cap until the pressure has been relieved. Remove cap once pressure has been normalized. If coolant begins to boil tighten cap back down and let the vehicle cool at bit. The idea here is we want the thermostat open so we can purge the entire coolant system.
Be careful, the coolant is likely in excess of 160*F and will scald the hell out of you. I will not be held responsible if you manage to cause bodily harm. 
Place the open end of the metal pipe into a container of sorts to catch any fluid that will come out.
Apply air pressure from a nozzle as illustrated above to the rubber hose, this will pressurize the coolant system. Continue adding air until you get more or less straight coolant emptying into your catch container or of course the coolant tank gets very low.
Best of luck!
The arrow in the picture simply denotes the direction the air should be going btw.
