Does Superman need to eat, breathe and sleep?

As long as he is under the radiation of a yellow sun, he doesn't need to eat or drink. I'm not entirely sure on the sleep part.

Superman can survive in space, so that means he can stay without breathing

Superman is immune to all non Kryptonian diseases, so that includes diarrhea. He probably is immune to some poisons.

Yes he needs all three; remember he is still a normal human at points, and having superpowers does not make you immortal. So maybe he could go even longer than the rest of us without any, but he does eventually need them.

I never heard of him being immune to poison or .....diarrhea (HOW CAN YOU BE IMMUNE TO THAT ANYWAY).

Depends on which version (some show him in space without needing a space suit)

But generally

He needs to eat

He needs to sleep (although I wouldn't be surprised to see him going straight for a few months without sleep).

But eventually he has to rest.

He's not immune to poison. Serve him a drink laced with Kryptonite. See the effects. As for ordinary poison, I don't think so.

Diarrhea... I have no idea.