What do you mean how well do you have to clean it? You have to clean and sanitize it just like you need to for your primary.
Unless introducing spices / fruit or some other addition there is no need to even put it into a secondary. (unless this is a beer that is going into extended aging) Leave it in the primary for three weeks and call it good.
OR - perhaps I am reading your question wrong. Are you planning on pitching on the previous yeast cake? You can pitch right onto it if you like, just sanitize the top / neck of the fermenter and your transfer equipment. This is of course assuming that nothing went wrong with that first batch.