When my beloved Patches was nursing her four kittens,
the food that the vet's staff said that I ought to be giving her gave her really bad diarrhoea, which left her absolutely covered in her own faeces as she laid in her cat bed with them. I changed her diet but then consulted the veterinary nurses (who, in turn, consulted the vet to check their advice) as to how to clean up my utterly filthy, very pongy cat.
Their advice was to stick to the rule about never washing a cat (unless, of course, its got a poisonous substance on its coat) and simply let her lick all the poo off. It wasn't long before she was looking beautiful again.
https://ukcatlover.rajce.idnes.cz/Patches_and_Her_Kittens/746327830