I have a 300 gal oil tank sitting idle and nominally empty and it occurs
to me it would be better employed as a water butt, looking ahead to
possible hosepipe bans etc. I can empty it completely but there would
still be some residue. How bad would it be for vegetable life if some
found its way onto their ground? I'm thinking that any oil residue would
float on the water till it evaporated, and the water would be drawn from
the bottom.

As a secondary question, is this heating oil the same stuff as paraffin?
Could I use it in a wick-burning paraffin heater? There seems to be
about 50 or so litres below the level of the outlet, difficult to
dispose of otherwise.

Brian Mitchell