My favorite stain remover, especially anything wtih fat/grease/oil is Spray and Wash Stain Stick. I put it on and let it sit a few days then wash in warm water. I have gotten out every imaginable kind of grease stain (I am assuming the stains are from the fat/oil/grease in the gravy). My husband works in a shop and gets black machine grease on his clothes, I have even been able to get that out without fail from all his woven shirts (by scrubbing with the edge of my nail, see below). We love cotton knit shirts but often fat/grease/oil stains just won't wash out. I have taken them, after drying them in the dryer, treated them, rewashed and the stains have come out.
Sometimes you have to put it on and take your fingernail and scrape at the stain to squeeze it (the grease) out of the fibers. The edge of a spoon also works. Place it on the top of your washer single layer and just scrape at it, back and forth, back and forth, using your nail or the edge or a spoon. Don't use a brush, it just makes the clothing fuzzy. Just be sure to put more back on, and I treat the front and back of a stain.
Nothing works better. I have stain sticks in both bathrooms, in the laundry room and my husband has one at work. But you can really rescue things that you missed and washed if you have to. I just try to get the stain as I am taking it off (thus the one in the bathroom) so it sits a few days in the dirty clothes with the stain stick working on the stain before I wash it.
Jann