Backflow Incense Cones It gets its name from the high tar content of smoke that produces in the process of burning flows from high to low like water. The backflow incense holder has a hole or a groove for the holes of incense, also conducive to smoke flow. Basics of Using Backflow Incense Cones First, light the tip of the incense cone, Hold for 4-6 seconds. Next , wait until smoke flows out of the hole in the back. Finally, extinguish lighter and place the cone on burner holder. Burn Time: about 8-10 minutes each incense cone.