A neighbour of mine works for a utility company and uses a large diesel van. I can often see him getting a large fuel container from the van and using a funnel to top up the small family car that he has.
He's not the sort to have a quiet word with - there would probably be something abusive coming back from him.
So, not right that he's doing this, and don't know whether I should turn a blind eye. However, all these sorts of things add to the cost of our fuel.
your neighbour is using fuel that doesn't belong to him, in other words he's stealing and if it's diesel the police will know by the colour of it, it's red, it's up to you whether you report him or not, I would Liz