Waste Suds

Can't you just take it to the local tip and pour it in the oil recycling? From an environmental side, that stops any risk of it getting into ground water and I can't believe the processing the do can't cope with anything no found in normal oil. Plus, the oil based parts will be recycled.

Decant it into a suitable container or simply put the bucket in a plastic bag. Deposit it in your dustbin and wait for it to be collected.

Let the council dispose of it in landfill where it will do zero harm, the landfill pits are commonly clay lined to prevent anything tipped getting into the water table and a few litres of oily gloop is neither here nor there.

P.S. If you dispose old engine oil at a council waste site and you wish to dispose of the containers you carried the oil in, then they are dumped in the general 'unrecyclable' waste skip that goes to landfill.