What do you used to wash your work clothes? We have a service, so I use that for the pants and shirt with my name, but I don't usually wear that shirt and end up washing my shirts at home. I think there is probably a better way that I haven't tried.
Well I prefer a washing machine to a washboard any day of the week... I don't know about your washer, but mine has a special option for very dirty clothes, so I use that and then use the extra rinse option too. I usually use hot water to cause I figure that will loosen the grease a little more.
How about this:
www.dickies.com/get-grease-out-of-your-workear.html
I might try the soda pop just for the heck of it