It's hard to believe that there are debates about making our waters cleaner... But I guess debates are good. I hope whatever method you choose is the most responsible disposal. "It is just a little amount of oil"... "What harm could it actually do?" But if everyone says that then that little amount is a big problem. It's like throwing a plastic water bottle overboard and then 5 minutes later complaining about how the waters are so polluted.
Most marinas support "clean environment" policy and will have methods of disposal that you can use or stop by your local gas station and ask their mechanic.
My two cents and I'm sure it's worth about that.