Formal:
* Toilet - This is the most common and widely understood alternative.
* Water closet - This is a more formal term for a toilet.
* Bathroom - This refers to the room where the toilet is located, not the toilet itself.
Informal:
* Toilet bowl - This is less formal than "toilet" but still refers to the actual fixture.
* Potty - This is a child-friendly word for a toilet.
Humorous:
* Throne - This is a playful and ironic way to refer to a chamber pot.
The best antonym will depend on the specific context and the desired tone.