My mother's (and now my) go-to for the hardest-to-clean stains is Fels-Naptha bar soap. You can probably tell by the dated packaging and low price point that Fels-Naptha soap is old-school.

This Bundle Includes a 5 Ounce bar of Fels-Naptha Laundry Bar and Stain Remover and a Hand Crafted Wood Soap Dish Giving your Laundry Area a Stylish Rustic Look. The Must-Have Laundry Soap Bar ...