how do i flush out my heater hoses and heater core. I have 2 heater units

What is your question?

My heater h oses were flushed out last year. the top hose and bottom hose to the heater core. There was a lot of gook inside of the hoses. Some heat was generated enough for me to keep warm and I was suppose to go back and have the heater core flushed and however the mechanic was going to do for the back heater. I did not go back and finally arround March the heat stop working again. My fault I did not have it rechecked. The fan is blowing cold air. The temperature gauge moves midway like the heater is working but it only blows cold air. I filled it up with antifree a couple of weeks ago. I tough both heater hoses and they dont even get warm now. The main big hose gets warm

What makes this problem better or worse?

nothing

How long has your 2001 Lincoln Navigator had this problem?