fill it full of water, block any escape holes, put it in the chest freezer, when the water freezes it expands , and will pop out the dint to its original form..
iv seen this done with dinted down pipes, on a internet linky some wear.
it worked down pipes , not sure about tanks .
up to you , will take no responsibility if ye tank explodes
found this on net too
<embed src="http://www.metacafe.com/fplayer/494805/remove_car_dents_with_a_dry_ice_block_www_mastrik_com.swf" width="400" height="345" wmode="transparent" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash"></embed><br/><font size="1">
<a href="http://www.metacafe.com/watch/494805/remove_car_dents_with_a_dry_ice_block_www_mastrik_com/">Remove Car Dents With A Dry Ice Block
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