When it comes to clothing stains, grease seems to be one of the more troublesome offenders. However, dishwashing liquid can make quick work of the grease, even if the stain itself is old.
Photo by Wikimedia Commons.
As tips blog The Kitchn points out, dishwashing liquid is already designed to break up tough gunk on your dishes. It can also work on your clothing. One Kitchn commenter points out that this only works with petroleum-based liquid, so if you're using a plant-based one, it may not work.