I made a custom tool for removing the big rings on the fuel tank, but once I couldn't find It and used a quick fix that I recommend for everyone else.

Take a bar of metal can be almost anything that is under about 1/2x1/8" flat or 1/4" round stock (12x3 or 6mm) about 12-15 in (30-40cm) and bend it into a "u shape" where the ends will hook onto the little steel loops on the giant fuel tank nut, now put anything long enough to fit through the U and turn while holding the (upside down) U into the "nut". You have perfect precise control; no risk of cracking a 15 yr old plastic fuel tank banging on it with a hammer.

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