Wouldn't worry too much for amateur use. The European Waste Catalogue is massive. My company for instance supplies insulating oil to go inside latge power transformers and oil filled 11kV switchgear. When the oil comes out for maintenance purposes it is generally no more "hazardous" than when it went in but it is still classed as a hazardous waste and has an entry in the catalogue.
Water authorites take a relaxed view over small domestic quantities washed down with plenty of water.
As Dave says keep re-using it as it goes on for ages.
Andrew
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Fenland Camera and Darkroom (Affordable Workshops)
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