I got this plastic tub at ACE Hardware for $6, it's way thicker than the ones at Lowes or Home Depot. A 5 qt size, the one I am using, should be enough for your average sedan. This trick only works if your levels are correct before you start. Do check your levels after filling to ensure you got things right, but this takes the guesswork out of "How much did I take out and how much do I need to put back in?"