At 160-190,000 miles our trucks had less than 1/10g estimated dirt at the bottom of the tank. One I didn't bother to clean out one I siphoned dry so I could weigh and get exact amount of fuel the sump holds. (5.0L: 1.4L shows on the gauge, 3.6L reserve below the zero on the dash gauge).

The reasoning for keeping > 1/4 tank doesn't apply at all to the e53. I was stranded twice on the freeway due to my wife's never letting tank get below 1/4 which allows the blown siphon o-ring go undiagnosed until you need the last quarter tank and you can't use it anymore.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)