In article ,
brian mitchell wrote:

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.


I'd be wary of letting oil residue onto land used for anything
I'd want to eat. I'd also be wary of letting fifty litres of
oil onto any land ever at all. Having said that, someone discharged
a can of old car engine oil onto land next door to me about five years
ago. To start with it killed everything within a half meter. Over
the next year or so I added a squirt or two of washing up liquid to
the soil at random intervals. Today, it would be hard to tell
where the oil was poured - maybe the soil is darker and less fertile
but I'm amazed how little damage it actually did.


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.

I should think it would be fine. Run it through a tea strainer to get
the lumps out and make sure there isn't water in it. I'd be less
happy about using it in a pressure paraffin burner.
It might fume worse than normal paraffin so don't use it for heating the
kids bedroom. I assume you're using for a greenhouse.