J.R.
Did the vet run any tests? My older cat (much older 9 years) had this problem and really it was the constipation that was causing the diarrhea. The liquid stuff was all she could get out. My vet did an xray to find the impaction, then she had to have an enema and now we give her lactolose a couple times a week (which just draws water to the colon) to help keep her regular. I couldn't find anyway to clean her at first besides bathing her butt - I just did her butt, not whole body. As she got a little better I was able to use wet rags. I did have a low lather shampoo, though, that helped a lot with rinsing.