As annoying as it is, you really should contact someone who knows the exact laws surrounding evictions for your exact situation in your city.

This could be a real estate lawyer or the tenant rights association where you live (Mietverband).

Tenants have a lot of rights in Switzerland and these rights vary depending on where you live. There are so many mistakes you could make trying to evict someone. As people mentioned, there are a bunch of things that apply to your situation:
- The communication has to use the correct official cancellation form and be sent with registered letter. Did you know that if the eviction / contact cancellation does not use the official cancellation form, the cancellation is void? (See Mietverband website.)
- The timing of the communication has to be correct.
- What you can and can’t do is very clearly regulated (i.e. changing locks, throwing things out on the street could get you in a whole lot of trouble.)
- The agreement you have may play a role (i.e. email, rental contract, handshake agreement).
- The length of time the person has lived with you may also play a part.
- There is a big difference between collecting the money you are owed and getting your guest / tenant out of your flat.
- Your guest / renter can challenge the eviction at the arbitration authority. If you do anything wrong (or in other cases, such as hardship) the renter could be granted more time.

The strong tenants rights (in this situation) might anger you and it would be really nice if the situation was as simple as telling someone who agreed only to stay a short time to get out or kicking out someone who isn't paying rent. Unfortunately, it isn't the case and you really need to tread carefully here.

Yes to the locks. Except to any spaces, such as bathroom, which are included in what he is allowed to use.

Move all your possessions out of any shared spaces and into your private rooms which you lock from the inside when you are at home, and lock from the outside when you leave the flat. It's very effective.

However, I wouldn't count on his learning anything such that you will want to continue sharing with him.

Keep your possessions safe while you give him formal notice in the correct way.

You could also just ask him to leave. You might find he's not happy either, and will just agree to go.

May not apply to such a case. You can't lock out someone for locking out's sake but you may be allowed to lock someone to protect your own possessions in crass cases such as this.

The first thing to do is get reliable advice. Berner's first stop should be the local Schlichtungsstelle, see here for Kanton Zürich.

Additionally, OP should inform his 3rd party liability insurance and the Hausratsversicherung, if any, and ask for advice/support. Asking to be burglared like this seems certain to affect insurance protection negatively.

Exactly.

This is what I meant. In our place, you can lock all the internal doors with keys so anyone who breaks in is pretty much restricted to the lounge and the hallway. Obviously we don't do this because we lock the external door, but it might help the OP keep the bulk of his stuff secure as well as provide the possibility to concentrate the mind of his devil-may-care room-mate.

How many seconds do you think it would take a burglar to kick down an internal door?

Not many, but opportunists don't like inconvenience and noise (can you imagine the clatter?? How long before some busybody is charging to your apartment to complain about the.. "Errr, where are you going with that telly?!!")

Plus (before anyone loses their mind) it was only an interim suggestion for an OP who seems to be otherwise fully exposed to burglars due to an unflushable room-mate.

just put locks on all the windows.