How to flush coolant system?

I am having trouble figuring out how to flush my 2000 Windstar coolant system. I have the heater inlet hose tee installed, the t'stat removed and the t'stat housing re-installed. What do I remove or open to let the 'flushing' water out as it back-flushes the whole system? That sealed 'pressurized' recovery tank and no radiator cap has me STUMPED!

Disconnect the lower radiator hose!

Forgive me for not 'getting it' but I'm still having trouble understanding what I'm doing. I'm at the point of installing a radiator flush product and did it by pouring it into the reservoir and proceeded to run the engine with a closed system for the time the instructions stated. My question: does the coolant circulate through the reservoir tank while the engine is running? It didn't look like anything was moving in that tank. If there is no substantial circulation through there my flush fluid is still sitting there and not doing me any good at all...where am I going wrong?? Give me the old radiator cap system any old day!

If you put it into the overflow bottle.....it will take some time for it to just get into the main system.
The instructions for how long to run the product.....are for how long to run it in the main system.
I would try to find a way to add the product into the main system......maybe drain much of the coolant out the petcock on the bottom of the radiator (is bottom, engine side, driver side on my '96)......and then disconnect the upper radiator hose and add it there.....in such a way to get it into the radiator....maybe with a funnel with a hose to stick into the radiator through the hose location.....then fill the system....and run the engine.....

CAREFULLY monitor the temperature throughout the process in case you have gotten air into the system.....and it could cause an air lock.......
If the temperature goes up too high....shut off the engine and let it cool....then check / fill the coolant system.....and run again.