how can i flush my heater rad in my 2004 ford freestar?

Flush the radiator with the heater on.

can you elaborate please....do you mean flush the heat rad while it is hot? I cannot get to the hoses...

The heater hoses run to the engine, just hook up there, you do not have to hook at the firewall. locate the heater hose leaving the block going to firewall cut the hose insert the tee connector for your hose size and hose clamp in place.

Also you can hook up in that hose anywhere you can, likely somewhere in the middle of that hose.

Watch: https://www.youtube.com/watch?v=WOu_Si3gdbs

You can buy a Prestone flush kit.