Dried feces all over cats behind and legs

Need help, one of my feral cat has dried feces, looks matted now, I tried wetting a paper towel and removing but it's very hard and she doesn't sit still for long. What should I do??

Not sure where you live, but is it cold there? If so, be careful how much water you put on her, wouldn't want her to have little icicles on her butt.   

I would just try to brush the clumps out with a fine tooth comb, or a flea comb for now. You could also consider getting her a "sanitary" shave during the spring/summer if this continues to be a problem. A groomer can trim just the hair on the rear legs and around the butt (not bald, just shorter.) It helps with long hair cats that get poop stuck. I definitely wouldn't try it right now if it's cold where you live. 

I use a fine tooth comb. It sometimes takes awhile as my ferals move around a lot and won't sit still, but I can usually get it all with a few tries.  I often bribe with a few treats or something yummy to eat while I work on the backside.

It is cold here. But, using a brush won't work it's completely hard. and she is feral. I don't know how I would trap her again to get groomed-they would have to sedate her in order to groom her at a vet which will cost me $$.

I am thinking of using dawn soap with warm water, and then putting vaseline on top...??