I put antifreeze in my ford windstar and it poured out as fast as i was filling it from the back of engine. Underneath. Could it be whose or something major?

Quite possible that you may have a cracked cylinder head or engine block. Just going to have to investigate further and hope its something a little less catastrophic, Like something on the heater system running down

probably a rusted out welsh plug

LOOK FOR A BURSTED COOLANT LINE TO REAR HEATER OR REAR HEATER CORE

If the antifreeze is leaking fast, then the most probable cause can be a hole or split in one of the coolant hoses. It is also possible for the radiator or water pump to have a leak. If you cannot see the leak when you inspect under the hood, then you may have to take the vehicle to your service repair shop where they can lift the van on a hoist to inspect underneath and they can pressurize the system to locate the coolant leak..

I wouldsuspect heater hose or a hose of some type. Parts store has a telescopic mirror that could be helpful in lacating where to find the leak.cheaper than pouring anti freeze on the ground

They are tough, all the way back under the engine opening-I use a clear hose attached to a funnel-the hose end goes into the reservior, the funnel end into the other, outside the enclosed area-pour into the funnel, with the hose in the tank, it is a pain, pour slowly.

filling order? what do you mean.. firing order? no idea what filling order is if talking about antifreeze just pour equal amounts of water and coolant if not 50 50 mix.. some are that way already read the label..

Maybe you didn't bleed all of the air out of your coolant systtem.
I had a very similar problem, last month, my heat would not go above 50 degrees F.

I had air in my heater core.

I put wheel blocks behind the back tires and engaged the emergancy brake.
I jacked the front of my van up so both tires were off the ground (about 3")
I removed the radiator cap, started the engine, and turned the heat on high.
I added antifreeze, until it was full.
I let the engine continue to run, as I watched the antifreeze level go back down, then I added more antifreeze.
After doing this 2 times, I squeezed and held the upper radiator hose. I did not release it.
I started pouring more antifreeze in and when it started to over-flow, I still kept pouring as slowly released the hose.
With the raditator level full, I replaced the cap and put some antifreeze in the coolant reservoir.
Lowered the front back to the ground and removed the tire blocks.
I stuck a guage in the inside vent and I now get a 125 degree reading.

Note...after I got the van jacked up, it only took me 15 minutes to get the air out of the system (mainly, because I squeezed and held the hose).

Sometimes you can rent tools from Autozone or Oreillys and get your money back when you return the tool.
What you want is a radiator pressure checker. With this tool you can pump up the system and the antifreeze will leak out of any hole or hose. You can do it on a cold engine and diagnose the leak safely. It can be something simple like a heater hose clamp or a leaking intake manifold.

Radiator has a cap indicating a running pressure of at least 15 PSI and could fill the Transmission cooler with engine antifreeze if there in a small crack or hole.