I always waste a little fresh oil and run it through (about a cup/250ml) just to give it a little rinse, hence why I had the filler cap off, and a rag to check the dip stick sitting on the air filter, and a funnel in the oil tube. I take my time, have a beer letting it drip as much used oil out as possible. I also usually run it for a minute or 2 prior to draining, getting it a bit warm for easy flow, and to mix it all up. Any thoughts on this? I had a mechanic once tell me it was a good idea, but also another that says it doesn't matter.