Use Dawn. I don't use it for anything other than removing oil from laundry now (I use a natural dish soap) but imho, nothing works as well for removing oil from clothing.
I personally didn't have luck letting my clothes sit overnight with the Dawn. I did much better scrubbing with a brush and rinsing immediately, then throwing it in the washer. When I let mine sit, I got larger oil spots where it had released and redeposited.
Perhaps, I left mine too long when I let it sit since it dried! However, when that happened, I tried again and rinsed/washed immediately and all came out!
I'd say just give it a shot and see which technique works for you. Either way, I think you'll be able to successfully get it out. Good Luck!