I had a good sport shirt, cotton and polyester, that for some reason I started wearing for a work shirt, a robe, and just about everything, and it got filthy in front. In the old days, 40 years ago and probably much less, I know it would not have come clean. This time I soaked it and another similar shirt in Clorox 2 for about 5 hours.
Then I drained the water, and I tried to tell if the shirts were clean, but when wet, it's probably impossible.
I washed them and other laundry in a detergent, which might have also helped clean them, and today when I took them outside, there was no difference from front to back!! Good as new.
BTW, I like my old machine where I have complete control of when it fills, drains, spins, Maybe some fancy new machines do all of this too, but I stayed in a rental house with what was probably a cheap machine, and once started there was no way to choose what part of the cycle you were in. I think all you could do is pause and resume. And which I can open when it's got water in it.
2) Very dirty.Why should the shirts above have been hard to clean? After all, the later dirt is on top of the earlier dirt, right? Does the later dirt protect the original layers of dirt from coming off the clothes? If not, then when the lower level of dirt is removed by the soap or detergent, the top layers should come off too.