My husband's work clothes are always quite nasty. He is a screen printer and his clothes are usually covered with ink, tack, glue, sweat and grease. Eww. There isn't much I can do about the ink. It is permanent and that is fine, they are just work clothes. The tack and glue just take some good, hot water. The sweat and grease, well, that is where the "booster" comes in.
My booster... liquid dish soap.
When you do a load of greasy clothes (work clothes, rags, kitchen towels/rags, sheets-for those of us with oily hair, etc.), wash in warm water, use your normal amount of laundry soap, and then add a good squirt of liquid dish soap. Not too much! About 1 to 2 tablespoons should do it. If you add too much, you risk creating too many bubbles for your washer to handle. No one wants a big mess of bubbles to clean up, although it would be quite fun for a while!
The grease fighters in the dish soap cut the grease in your clothes just as well! It is inexpensive as well. Can't beat that!