The operator usually does not have to cut access into the duct with this method. The operator inserts the brush & vacuum into the duct using an existing vent opening. The operator pushes the spinning brush and vacuum into the duct to "scrub" and "vacuum" away the dirt, dust, and debris. Note: This website recommends the Rotary Brush type method for residential & light commercial.
Now here is the thing: There are many rotary brush air duct cleaning systems on the market today. Make sure you research the systems out there. There are differences that make some systems better than others. For example: Many systems out there have the brush attached directly to the vacuum hose. How will you make the twist and turns of ductwork with a big vacuum hose? If you are choosing the rotary brush method, make sure you find a system that will easily maneuver through the duct. A system that separates the brush from the vacuum will allow more maneuverability. Remember, you are not sucking all the stuff back at you like Negative Air, you need to have maneuverability in the system to scrub all the duct.
Website Rotary Brush Air Duct Cleaning System Recommendation: SpinVax 1000 Package by CleanCraft Products, Inc.
Compare Rotary Brush to Negative Air Methods: "Types of Air Duct Cleaning Equipment"