'desperate imo [buying] that [heavily dented tank'
isnt just the $, rather the badly dented tank..
i wouldnt take it if you gave it to me,,
unless, desperate.. ie, no other options..
for starters its internal sealing material
is compromised, thus more susceptible
to rusting effects of ethanol blended fuel..
'how do you know' ethanol blended fuel [?];
in aust similar to usa and suchlike societies
petrol outlets are required to label petrol products
containing ethanol.. for starters ethanol is not,
suitable for marine or light aircraft engines..
based on obvious safety issues given
known engine failures..
in aust its E-10 [ethanol 10%] labeling
on pumps with 'regular unleaded' [91RON]
the base petrol for all octane graded petrols,
to which is blended 10% ethanol for 'E-10'
here plus an extra 17c additive package = '95'
and for another 7c additive package = '98'
here the expensive options have no ethanol..
thus motorists are forced to pay more
to avoid putting ethanol in their engines..
based on a govt mandate, based on a monopoly
by one company, which donates heavily to politicians..
fortunately some outlets [eg my caltex south coogee]
continue to supply unpolluted petrol..
theres a map of usa outlets for clean petrol,
including marine 'recreational' petrol..
in 2016 over 60 countries were blending ethanol..
Biofuels Mandates Around the World: 2016 : Biofuels Digest