This product is available Walmart, Kmart, etc., and it does work well. Here is their marketing blurb:
How to treat laundry problems with De-Solv-it® Citrus Solution™
When using any product with laundry, first check for colorfastness of fabric (in an inconspicuous area). Apply De-Solv-it® CITRUS SOLUTION™ to both sides of fabric and work gently to blot and remove. Rinse any remaining residue under faucet before reapplying and laundering. Apply TIDE® liquid detergent (recommended) on problem area before laundering. Detergent actually helps lift challenge and De-Solv-it® from colorfast material in wash cycle.
Basically the Desolvit dissolves the stain, but then you have to get the desolvit out. Soak in desolvit, gently use a toothbrush to help penetrate, and keep a towel under the fabric to help absorb anything coming through. I use Shout on the Desolvit myself, anything that cuts grease well works. You can hand rinse with detergent and water, and repeat if necessary. Launder/dry after the stain is gone.
I've done this on DH's shirt and pants. Even ones he's already washed and dried
[Also used it to get paint off of carpet, etc. Once the problem is dissolving, you have to blot it up quite a bit, but it's the blotting up with soap and water that really pulls it all out.]