flea dirt after flea treatment

my new cat (just got him today! ) has flea dirt in his fur near his tail. I can't see any fleas. I looked in a couple places and he has white fur so it should be easy. He was from the shelter and they treated him with frontline July 1st. So he'd be due for another dose I think , right? But how do I remove the flea dirt? Would a flea comb work? I kinda hate to try a bath yet, since we just got him. I don't want to terrorize him. 

Yes he would be due again, and the flea dirt will go away with his own grooming in time, however you can brush him regularly and it eventually all gets dislodged and falls off.

Flea dirt/poop is actually dried blood feces from fleas. So if you were to take a wet cloth and swipe it, you will see red.

I agree in not trying the bath thing just yet!

Thanks for adopting a shelter cat. You have saved his life