We've never seen the Tardis toilet but I think that among its myriad of rooms, there must be one somewhere! But perhaps Time Lords don't excrete waste in the way we do, so maybe he doesn't need one...

As far as I know, Babylon 5 is the only sci-fi series that ever showed a toilet.

I guess the characters of the other shows just don't need to go at all, otherwise you'd think a toilet would have been mentioned by now.

It probably does have a toilet it's just never been mentioned.

There is an outback loo.