What is a good method to clean an oil fired hot air heat exchanger?

I have done this before, just want a refresher. Is there something online or if you have a procedure that you go by? I remember vacuuming and dumping out a flue pipe years ago. And I recall using a brush inside. Just trying to get my head together. They want $160 to do this in our area and fuel is high enough and I am on fixed income. I am mechanically inclined, have tools, vacuum cleaner, etc.