How to kick out an alcoholic?

As a college student I'm still living at home (planning to move out in the next year). My mother's boyfriend's son is 26 (5 years older than me) & very kind. He's been allowed to crash on our couch plenty of times in the past, but recently he's stopped helping around the house to compensate and has kept himself wasted for over a week straight. No one wants him here anymore and we all plan to politely confront him later today with an intervention, but none of us have any experience kicking someone out before. He's always been nice, so we're unsure how to tell him we want him out without coming across as cruel. 

What should we say? How do you politely kick someone out?

(for reference, he is absolutely an alcoholic & has been for years, we're kicking him out because of how bad it's gotten but not for the alcohol itself, he's been allowed to stay here drunk plenty of times before)