This is a good question

Did he have kronk pull the lever?

One possibility is that by saying "Stairs" in Parseltongue, stairs would have formed the same way the chamber opens when "Open" is said in the snake language.

Ever notice how big the pipes around Hogwarts must be? How big did they expect the shits to be? Judging by the relatively small number of bathrooms in the castle it can't be quantity they were afraid of.