Personally I use up about a litre of new oil after the old oil is drained out. Once there is no more old oil to come out from the sump, I put back the nut hand tight then pour in another litre and fire the engine up for 40 seconds. Some people think its crazy to start it up without much oil, but the funny thing is there is alot of old oil still in the block, and the thicker gunked oil stays in the upper rocker. Once you undo the sump nut you will be surprised how much oil has sunk back into the sump.
After that I still add another 500ml of oil until the sump runs clear and I know its clean.
I've done this for about 13 odd years after seeing an old boy do it, and I've never had any engine I've owned suffer from this.
Plus any cars that have paper oil filters when you drain the oil let as much pressure out helping the old oil make its way down, like removing the oil filler cap and oil filter housing lids!
