For such a small quantity, just take it to your local council tip and put it in their motor oil recycling tank. They won't thank you for it, but it works.
For larger quantities, or if you are being good, put it in a black plastic bucket or dustbin, protected from the rain. Fish out any ice that forms in Winter and wait until the summer sun evaporates most of the water, then do as above. A small garden fountain and/or fish tank heater will speed things up a bit.
I've got rid of 30 gallons of the stuff the second way.