Cleaning bottom

Should I be cleaning my cat's bottom? Sometimes I'll see some black spots around his anus and then a few days later, it's gone. So I'm wondering it's better that I do it or let him do it? Although, I don't know how he can possibly reach all the way back there! 

If so, would warm water and a towel be good enough? Or do I need those pet wipes?

I only clean my guys if something gets caught on the fur (usually following an upset tummy). Washcloth and warm water is fine, but I find they sometimes tolerate baby wipes better. Most aren't great for pets, but there's a brand called Water Wipes (I know amazon sell them, don't know other US stockists though) that are very pure. I first got them to use for the pony, but they work great for cats too - at least, Asha didn't complain too much :lol3: