I flush it. I use a piece of cardboard (filter box) tucked up under the oil filter mount. using a measuring cup I run the motor till I have drained 2 cups from the motor. I then install the filter prefilled, add 2 cups of oil to the oil bag start the engine, run for a minute, then top off the oil level if necessary. This is done after I have drained and refilled the oil bag with fresh oil. This process works on EVOs. Do not do this on a twin cam. You will do major damage to your engine.